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This photo shows the Southern Cross computer
hooked up to the 8x8 LED display & to the simple
RS232 interface of Fig.2 which has been built up
on a small piece of Veroboard.
Peripherals for
the Southern Cross
Z80 computer
This month, we present a number of
peripherals for the Southern Cross Z80
computer which was featured in the August
1993 issue of SILICON CHIP. We look at ways
to connect the Southern Cross to a personal
computer to make it easy to write programs,
introduce an 8x8 LED Matrix display
board which can produce interesting visual
messages & describe an EPROM emulator.
By PETER CROWCROFT & CRAIG JONES
62 Silicon Chip
While it is desirable to learn how
to enter machine code using the hex
keypad of the Southern Cross computer, it is much easier to write these
programs on a personal computer and
then download them for testing.
The fast way to write such programs
is to use a text editor on a PC and
then use a Z80 assembler to produce
a file suitable for downloading to the
Southern Cross. A public domain Z80
assembler, Z8T, is supplied with the
Southern Cross kit and produces what
is called an Intel hex output file. This
is an ASCII file with a checksum every
16 data bytes and other information to
help ensure that the transmission can
be checked by software at the receiving
system.
+5V
+5V
4.7
RTS
V+
1
C1+
DSR
PC SERIAL
PORT
DB25
TXD
RXD
16
TXD 2
VCC
4
C2+
1
13
14
Q2
BC547
4.7k B
6.8k
1
3
47k
D1
1N4148
10
2
CTS
PC SERIAL PORT
DB25
IC1
C1- MAX232
C2-
R1IN
R1OUT
T1OUT
V-
T1IN
GND
6
SOUTHERN
CROSS
BIT PORT
CN4
5
12
11
RTS 4
SOUTHERN CROSS
BIT PORT CN4
E
2.2k
DOUT
RXD 3
4.7
GND
B
+5V
DSR 6
15
SG
E
D2
1N4148
CTS 5
DIN 1
DIN 1
C
SG 7
C
Q1
BC547
C
VIEWED FROM
BELOW
4.7k
DOUT
E
GND
Fig.1 at left is the ideal circuit for an RS-232 serial interface as the MAX232 IC is designed for this job.
However, most RS-232 applications for an RS-232 interface for the Southern Cross will be satisfied by the
transistor circuit of Fig.2 (right).
There are basically two ways to
connect the Southern Cross to a
PC. First, you can connect it to the
serial or parallel port of a PC and
download the assembled program
from the PC into the RAM space
(2000H to 3FFFH). Second, you can
use an EPROM emulator. In this case,
the assembled program is moved to
the emulated ROM space (2000H to
3FFFH.) The Monitor uses almost 4K
of ROM so there is 4K free for you to
use for your own programs.
Serial downloading
Assuming that you have written a
program on your PC and have created
an Intel hex file using the Z80 assembler, you will then want to download
the hex file to the start of RAM (2000H)
on the Southern Cross.
By the way, making the jump from
a raw novice to being able to write
such programs will probably take
several weeks at least, assuming that
you can devote plenty of time to your
Southern Cross, once you have it up
and running. We certainly do not make
light of this achievement but we feel
sure that most people who purchase
the Southern Cross will do it.
The serial port on the Southern
Cross is on connector CN4. Unfortunately, this cannot be connected
directly to the PC serial port, since it
operates on 12V while the Southern
Cross operates at 5V. An interface
board is required and two such inter-
face circuits are shown in Figs. 1 &
2 – see above.
For reliable serial communications,
the guaranteed way is shown in Fig.1,
using a MAX232 IC. A much simpler
circuit is shown in Fig.2. This should
be adequate in most cases but cannot
be guaranteed for all situations. It can
be assembled onto a small piece of
Veroboard. Three wires are required
between the PC and the interface
board, while four wires extend from
the interface to the Southern Cross.
To download the file we must do two
things: prepare the Southern Cross to
receive the file and then get the PC to
send the file. On the Southern Cross go
to the address you want to put the file
and press Function 1. The Southern
Cross is now in ‘ready to receive Intel
Hex file’ mode. To send the file from
the PC you should first make sure that
its serial port is not already being used
by a mouse or other hardware item.
Next you must set up the port with
the DOS command:
MODE COM1: 4800,N,8,1
This sets the PC’s port to 4800 baud
to match that for the Southern Cross
which is set to 4800 baud in the Monitor. Then enter the DOS command
COPY filename.hex com1:
This starts the file transfer. Alternatively, you could use a communications program, if you have one.
When the Intel hex file is fed to the
Southern Cross, the Monitor checks
that it has been received correctly and
converts it into machine code in the
correct memory locations. If the transfer was successful a ‘C’ is displayed.
Press any key to return to the Monitor.
The downloaded file should be in
RAM at the address (usually 2000H)
it was sent to. If an error has occurred
an ‘E’ will be displayed. If it did not
come down at all, then nothing will
be displayed.
The baud rate for file transfer may
be changed in software as outlined
in the user manual supplied with the
Southern Cross.
8 x 8 LED display
This add-on board allows you make
your own moving message displays.
One or two display boards may be
Parts List for the
8x8 LED Display
1 PC board, 108 x 60mm
1 CMD-58813 8x8 LED display
2 74HC273 octal D flipflops
(IC1, IC2)
1 UDN2981 cathode driver (IC3)
1 ULN2803A anode driver (IC4)
1 DPDT slide switch (S1)
1 10µF electrolytic capacitor
2 18-pin IC sockets
2 20-pin IC sockets
1 16-pin box header connector
1 16-pin IDC socket connector
1 500mm length of 16-strand flat
cable
December 1993 63
1
10
VCC
D7
D6
D5
D4
D3
D2
ROW LATCH
I/O SELECT
D1
D0
83H
S1a
1
3
14
5
12
6
11
7
10
8
9
2
15
16
4
13
VCC
20
CLR
O8
18 D8
17 D7
O7
9
19
1
16
4
14 D6
ROW O6 15
13 D5 LATCH
12
8 D4
IC1 O5
74HC273
9
7 D3
O4
4 D2
6
O3
3 D1
5
O2
11
82H
O1
CLK
82H
2
5
8
7
6
3
2
O1
I1
I4
I5
O4
I7
O5
I3
O8
83H
O7
11
IC4
UDN2981A
10
14
ANODE
DRIVER
I2
15
I8
I6
LD1
CMD-5881F
18
12
D4
D3
D5
O6
D2
13
D6
D1
O3 16
D7
D8
80H
O2
81H
RESET
17
18
GND
VCC
GND
20
SOUTHERN
CROSS
I/O PORT
D7
D6
D5
D4
COLUMN
LATCH
I/O
SELECT
81H
S1b
80H
D3
D2
D1
D0
18
O8 19
16
O7
15
14
D6
O6
13
12
D5
O5
9
8
D4 COLUMN O4
LATCH
6
7
D3
O3
5
4
D2
O2
IC2
74HC273
3
2
D1
O1
11
CLK
17
1
D8
D7
1 I1
4
5
O1 18
15
O4
O5 14
I4
I5
CATHODE
11
DRIVER O8
I7
O7 12
6
13
IC3
I6
06
ULN2803A
3
03 16
I3
2
17
O2
I2
8
7
I8
9
CLR
10
8x8 DOT LED MATRIX
Fig.3: the 8x8 LED matrix display is driven from the parallel port of the
Southern Cross computer via two Tri-state latch ICs (IC1 & IC2) & two buffer
ICs (IC3 & IC4). Switch S1 switches the latches between two sets of port
addresses, thus allowing two LED matrix displays to be used together.
used and they are connected to connector CN1 of the Southern Cross. Each
board is designed so that the display
section may be cut away from the
circuit section and connected by flat
ribbon cable.
The circuit of the 8x8 LED Matrix
display is shown in Fig.3. It is connected to the parallel I/O port of the
Southern Cross via connector CN1.
Data lines D1-D8 are used to drive two
74HC273 octal D-flipflops, each used
as 8-bit latches (IC1, IC2). The eight
outputs of the two latches are buffered
by the UDN2981A anode driver (IC4)
and ULN2803A cathode driver (IC3),
64 Silicon Chip
respectively. These drive the rows
and columns of the 8x8 LED matrix
display. Latch IC1 is also connected
to the system Reset to ensure that the
LEDs are not lit when the circuit is
first powered up.
Slide switch S1 switches the latches
between two sets of port addresses. In
this way, two LED Matrix displays can
be used together, one operating from
port addresses 80h and 82h and the
other operating from port addresses
81h and 83h.
The LED Matrix display is multi
plexed and relies on persistence of
vision to produce its complex patterns
so that moving messages (for example)
can be displayed. In the kaleidoscope
program, each LED may seem to be on
all the time but it is not. Each LED is
turned on for only 15 microseconds
every half a millisecond. This is a duty
cycle of 3%. Peak current through the
LEDs is 70mA but the average current
is only 2mA.
Constructing the LED display
Assembly of the LED display board
does not involve many components
and should not take long at all. The
component layout diagram is shown in
Fig.4. First, fit the 11 wire links to the
board. Some of these may be hard to
spot. Don’t forget the two short links,
near the slide switch.
Fit the LED display so that its out-
LD1 CMD-5881F
D7
1
D6
D5
IC3
ULN2803A
D4
D2
10uF 1
IC2
74HC273
1
The 8x8 LED display is, as its name suggests, a matrix of 64 LEDs which
are driven in multiplex fashion from the parallel port of the Southern Cross
computer. Note the slide switch to change the address of the display, so that
two can be used in conjunction with each other.
line matches the screen printed outline
on top of the board. This is most important because if you do it the other
way around the display will be upside
down and won’t work.
Sockets are supplied for the four
ICs and these can be soldered in next.
This done, fit the 10µF capacitor, the
slide switch and the rightangle flat
cable connector.
You will have to make up the 16
way cable which uses IDCs (insulation displacement connectors. These
are squeezed together with a vise to
apply even pressure to the connector
halves.
When you finish each connector,
inspect the pins closely to be sure
that each pin is connected to the
cable strand that it is supposed to go
to. It is rather easy when doing hand
construction of these cables to find
one pin has gone in skewed and is
shorting between two adjacent V-pins.
Make sure that pin 1 at one end of the
cable goes to pin 1 at the other end,
and not pin 16.
To check that the board is working
the Southern Cross monitor has a
kaleidoscope built into it. Put the
switch in the up position. This will
connect the two latches on the board
to ports 80H and 82H. Press Function
E. (To remind you – press the Reset
key, then the Fn key then the ‘E’ key.)
A pattern of ran
d omly generated
D1
D0
IC4
UDN2981
IC1
74HC273
1
S1
symmetric images should appear on
the display. This will continue until
Reset is pressed.
Programming the 8x8
Multiplexing the 8x8 can be done
in several ways. One of them is to use
the subroutine already written in the
Monitor. In this subroutine, SKATE,
one row of 8 LEDs is scanned at a time.
The LEDs to be turned on in that row
are given by the bit pattern of the 8
positions. A bit pattern of 10000001 (or
81h) will turn on the outer two LEDs.
A pattern of 11111111 (FFh) will turn
them all on.
To program this, the byte representing the top row is stored in the register
pair HL. HL+1 stores the byte for the
second row from the top, HL+2 the
byte for row 3 etc. We can conveniently use system call 16 to scan the 8x8
display rather than re-invent the wheel
and write our own code. An example
will show this more clearly.
Using a piece of paper, form the
letter A of your choice using the 8x8
SOUTHERN CROSS
I/O PORT
Fig.4: the component layout of the 8x8
LED matrix display. Do not omit the
very short links on either side of the
slide switch.
matrix. We decided on codes 18, 24,
42, 42, 42, 7E, 7E & 42 as follows:
00011000 = 18h
00100100 = 24h
01000010 = 42h
01000010 = 42h
01000010 = 42h
01111110 = 7Eh
01111110 = 7Eh
01000010 = 42h
Do you see the capital A outlined
by the 1‘s in the code above and how
to derive the hex byte representing the
0 & 1 pattern? Hand enter these bytes
into locations 2000h to 2007h of the
Southern Cross. Next, enter the code
shown in Table 1 at 2100h, then do
Fn 0. You should have the letter “A”
displayed on the LED matrix.
Table 1
2100
2103
2105
2106
21 00 20
0E 16
F7
C3 00 21
LD HL,2000H
LD C,16H
RST 30H
JP 2100h
;point HL to buffer
;system call SKATE
;call it
;repeat the loop
December 1993 65
33pF
RESET
S1
33pF
X1
6MHz
1
330
TO PC
STROBE
6
ERROR
7
BUSY
8
D3
5
D2
4
D1
3
D0
2
GND
1
3
2
4
7
30
29
28
27
34
33
1
P14
A
K
DIPSW
31
IC1
8748
2
1
B
C
330
LED2
READY
10k
10
37 A14
36 A13
35 A12
24 A11
23 A10
22 A9
21 A8
11
19 DB7
18 DB6
17 DB5
16 DB4
15 DB3
47k
B
Q1
BC547
5D
6D
7D
8D
20
VCC
5O
6O
7O
8O
16 A4
15 A3
14 A2
13 A1
12 A0
E
C
VCC
11
4
10
1
OC
TARGET
RESET
D1
1N4148
C
4D
IC2 4O
74HCT573
17 A5
3D
3O
3
18 A6
2D
2O
2
19 A7
1D
1O
5
6
7
8
13 DB1
14 DB2
9
12 DB0
VIEWED FROM
BELOW
3
4
32 39
WR
P26
P25
P24
P23
P22
P21
P20
ALE
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
5
P15 T1
SS
EPROM EMULATOR
38
XTAL2
P27
XTAL1
RESET
EA
P13
P12
P11
P10
P17
P16
TB
26
VDD
6
INT
27
1
26
2
23
21
24
25
3
4
5
6
7
8
9
10
WE
A14
A13
A12
A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
28
20
CE
IC3
62256
VCC
14
D7
D6
D5
D4
D3
D2
D1
D0
18 D7
17 D6
16 D5
15 D4
14 D3
13 D2
12 D1
11 D0
A14 17
A12 16
A13 15
A8 14
A9 13
A11 12
A10 11
A0 18
A1 17
A2 16
A3 15
A4 14
A5 13
A6 12
A7 11
D4
D3
D2
D1
20
VCC
O4
O3
O2
O1
14
15
16
17
18
7
10
20
E1
E2
1
19
B1
B2
B3
B4
B5
B6
B7
A7
A0
VCC
20
10
E
19
10
A1
A2
A3
A4
IC6 A6
74HCT245 A5
DIR
1
19
D7
D6
D5
D4
D3
D2
D1
D0
A0
A1
A2
A3
A7
A6
A5
A4
VCC
3 A14
4 A12
5 A13
6 A8
7 A9
8 A11
9 A10
2
VCC
9
A7
8
B6
A6
7
B5
A5
6
IC5
A4
B4
74HCT245
5
B3
A3
4
A2
B2
3
B1
A1
2
A0
B0
E
1
DIR
B7
D5
IC4 O5
74HCT541
13
D6
O6
9
11
O8
D8
12
8
O7
D7
6
5
4
3
2
D5
D4
D3
D2
D1
D0
28
VCC
A5
A4
A3
A2
A1
A0
47k
NETWORK
D6
4
3
1
2
14
5
VCC
A14
A13
A12
A11
A10
A9
A8
A7
A6
5 A5
6 A4
7 A3
8 A2
9 A1
10 A0
VCC
4
A6
28-PIN
3
D7 EPROM A7
SOCKET
25
22
OE
A8
24
20
A9
CE
21
A10
23
A11
2
A12
26
A13
27
A14
19
18
17
16
15
13
12
11
A12
10k
A14
LED1
DATA
A11
A13
66 Silicon Chip
The EPROM emulator can be used with the Southern Cross or any other 8-bit computer for that matter.
It can emulate 8K, 16K or 32K EPROMs.
EPROM emulator
▲
This replaces the EPROM in a
computer system with RAM. It has a
28-way cable and 28-pin header plug
which takes the place of the EPROM
in the target computer. In our case, the
target computer is the Southern Cross
but it could be any computer system
which uses an 8K, 16K or 32K EPROM.
The RAM imitates or emulates
the EPROM. The target system reads
the RAM and thinks it is reading an
EPROM. Essentially, it is an independent block of RAM which can be access
ed from two sides: (1) from the target
Fig.5 (left): the EPROM emulator uses
an 8748 microcontroller (IC1). This
takes data from the host computer a
nibble (four bits) at a time & stores it
as 8-bit data in a 62256 static RAM
(IC3). The target computer then “sees”
the RAM as a normal EPROM.
X1
2x33pF
1
10k
1
1
IC4
74HCT245
1
10k
1
IC2
74HCT573
This example demonstrates how
using the subroutines in the Monitor
simplifies code development and
reduces time. Just four lines of code
have put the contents of the 8-word
buffer on the display. Add some bit
shift instructions, delays and a bigger
message buffer and you can move a
message across the screen. Or you can
develop a maze game.
Examples of each of these types of
programs, a maze game and a scrolling
message program, have been supplied
on the floppy disc which accompanies
the 8x8 kit.
Now let us look at the last peripheral
to be described this month, the EPROM
Emulator.
1uF
TO PC
1
IC3
8748
IC6
74HCT541
0.1
1
DIPSW
47k
Q1
330
S1
OUTPUT
TO
EPROM
IC5
74HCT245
IC3
62256
330
0.1
4x47k
D1
LED2
LED1
Fig.6: the component layout for the EPROM emulator. Note that all the ICs
are mounted in sockets & must be oriented exactly as shown. The device is
connected to the Southern Cross computer via a 28-way flat cable fitted with
28-pin DIP headers.
system which can read from it; and (2)
from the host PC which can write to it.
Hardware and software make sure that
simultaneous access from both sides
is not possible.
The advantage of this system is that
program development time can be a
matter of seconds rather than tens of
minutes or even hours under the old
blow-and-erase cycle. The RAM can
be written to by the external computer, so the target system immediately
sees a ‘new’ EPROM. In addition,
the emulator gives the capability to
download and test other programs in
its unused RAM.
The emulator described here is an
‘intelligent’ design with an 8748 (or
8749) microcontroller and, as already
noted, it can emulate 8K, 16K or 32K
EPROMs. A floppy disc with a public
domain Z80 assembler is provided
as well as a Monitor for the Southern
Cross and program examples.
The principle of operation is that
the program to be tested on the Southern Cross is prepared and assembled
in your PC. It is then downloaded to
the emulator. While it is being down
loaded, the Southern Cross system
is held in RESET state. When the
trans
fer is successfully completed,
a message appears on the PC screen,
the Southern Cross system is released
from the RESET state and then it is
in control.
The circuit diagram of the emulator is shown in the diagram of Fig.5.
Only four of the eight available data
lines from the parallel port are used to
transfer data from the PC to the emula
tor. This results in a saving of two ICs
and the elimination of a DB25 port
connector on the emulator PC board.
The speed cost is about a 10% reduction in data transfer rate compared
to that possible if all eight lines were
used with DOS commands to do the
transfer. This was judged to be an
acceptable trade-off in this instance.
December 1993 67
Table 2
IDC Pin
Name
Male Sub-D Pin #
Cable Strand #
1
Ground
18-25
1
2
Data line 0
2
3
3
Data line 1
3
5
4
Data line 2
4
7
5
Data line 3
5
9
6
Strobe
1
10
7
Error
15
8
8
Busy
11
9 & 10
Not Connected
6
4 & 2 resp.
Prices & availability
Since the first article on the Southern Cross in August 1993, the prices for
the kits have needed to be adjusted to compensate for currency movements.
The prices are as follows:
Southern Cross Computer ..................................................................$194
Dallas 1213B SmartSocket ...................................................................$63
Dallas 1216B SmartSocket ...................................................................$84
8x8 LED Display ....................................................................................$73
EPROM Emulator ................................................................................$129
Technical manual of IC data sheets ......................................................$12
The kits containing all the components may be ordered in Australia from
Alpine Technology, PO Box 934, Mt Waverley, Vic 3148. Phone or fax (03)
751 1989. You may pay by Bankcard, Mastercard, cheque or money order.
Buyers outside Australia should contact DIY Electronics in Hong Kong.
Phone/fax (852) 725 0610.
The emulator board, emulator software and the software which you are
already using in your PC must combine together to operate the EPROM
emulator.
Power for the emulator comes from
the Southern Cross via the 28-pin
socket. The 2-way DIP switch selects
the size of EPROM to be emulated.
The simple RS-232 interface of Fig.2
can be built up on a small piece of
Veroboard as shown here.
68 Silicon Chip
To emulate the Southern Cross (8K
EPROM), both DIP switches will be in
the OFF position.
The 8748 microcontroller receives
the program from the PC a nibble (4
data bits) at a time. It assembles them
into bytes (8 data bits) and generates
the address and all the timing signals
to write the byte into the 62256 static
RAM. It also controls the target (ie, the
Southern Cross) system via the RESET
line, reads the DIP switches, and communicates back to the PC.
IC2 is a 74HCT573 Tri-state octal
D-type latch which is controlled by
the 8748 to switch data from the four
input data lines into the addresses
of the static RAM (IC3). IC4, IC5 and
IC6 are also Tri-state chips which are
controlled by the target computer (via
the 8748) in accessing data stored in
the RAM when the circuit is emulating
EPROM.
Construction
All the components are mounted
Parts List for the
EPROM Emulator
1 PC board, 114 x 58mm
1 6MHz crystal
1 2-way DIP switch
1 miniature momentary contact
switch (S1)
1 200mm-long 28-strand ribbon
cable
1 150mm-long 10-strand ribbon
cable
2 28-pin DIP headers
1 10-pin IDC connector
1 10-pin box header connector
1 25-pin male sub-D connector
1 25-pin sub-D case
1 40-pin IC socket
1 28-pin IC socket
4 20-pin IC sockets
Semiconductors
1 8748 microcontroller (IC1)
1 74HCT573 octal Tri-state D
flipflop (IC2)
2 74HCT245 octal Tri-state
transceivers (IC5, IC6)
1 74HCT541 octal Tri-state buffer
(IC4)
1 62256 static RAM (IC3)
1 BC547 NPN transistor (Q1)
1 1N4148 signal diode (D1)
1 3mm yellow LED (LED 1)
1 3mm green LED (LED2)
Capacitors
1 1µF electrolytic
1 0.1µF monolithic
2 33pF ceramic
Resistors
1 47kΩ SIL resistor network
1 47kΩ ¼W
1 10kΩ ¼W
1 330Ω ¼W
on a double-sided PC board which
is screen printed on top to show the
layout – see Fig.6. Sockets are used
for all the ICs and these can be placed
and soldered after all the small components are inserted. Make sure that the
transistor, the two LEDs, the diode and
the electrolytic capacitor are inserted
with correct polarity.
A single wire connects the “TO
TARGET RESET” pads of the emulator
to RESET on the target system.
Two cables with IDC connectors
need to be made up. One cable
Continued on page 88
formed per second. Input impedance
is 1 Gohms and inputs are protected
against over voltages to 200V. There
is also a 4-bit isolated output port
provided.
The LLAD 140 is a 2/3-length card
and comes supplied complete with
user manual and utility disc. Interfacing is via a DB-15 connector located
on the end of the board.
For more information, contact Boston Technology Pty Ltd, PO Box 1750,
North Sydney, NSW 2059. Phone (02)
955 4765.
Australasian
satellite TV book
Written by Mark Long and
Jeffrey Keating, "The World of
Satellite TV" gives a comprehensive description of the technology
involved in the delivery of satellite
TV. It also explains why some
installations need big dishes and
gives with actual footprints and
transponder loadings for satellites
in our region.
This second edition of "The
World of Satellite TV" has been
accepted by many as the best
satellite book available. It can
be purchased from Dick Smith
Electronics, Jaycar Electronics or
Peter C. Lacey for $29.90 plus $5
pack and postage. The Australian
distributor is Peter C. Lacey Sermodule is $299.00. Both modules are
rugged circuits with the well-proven
Hitachi Mosfets. Get into them while
they last. They're available at A-One
Elec troncis Pty Ltd, 432-434 Kent
Street, Sydney NSW 2000. Phone (02)
267 4819.
Low cost 15-bit
4-channel A/D card
Boston Technology Pty Ltd has announced the Australian release of the
Low cost PC board
prototypes
vices Pty Ltd, 80 Dandenong Road,
Frankston, Vic 3199. Phone (03)
783 2388.
LLAD 140 15-bit 4-channel A/D card
for PC/XT/AT/386/486 and compatible computers.
The LLAD 140 analog interface has
four differential analog input channels, each with 0.25mV resolution
over an input range of ±5 volts, with
excellent stability and noise immunity. Standard linearity is 0.005%.
Reproducibility is ±1 count or better.
Readings are accurate to within .025%
of full scale at normal operating temperatures, and 7.5 conversions are per-
Southern Cross Z80 Computer – ctd from p.68
connects the 10-pin IDC socket with
the 25-pin Centronics sub-D male
connector using 10-strand flat cable.
The other cable connects the 28-pin
EPROM socket on the target system
to the 28-pin EPROM socket on the
emulator board.
Two identical 28-pin DIP plug connectors have to be connected to either
end of the 28-strand flat ribbon cable.
You need to decide on the cable length
which should ideally be no more than
200mm long. The method of making
these cables is described above.
The parallel port cable has eight
connections as listed in Table 2.
Make the 10-pin IDC socket connector first. To do this, match cable strand
1 (usually hatched red colour) to the
triangle pin 1 moulded in the IDC
socket. Press the socket together, then
88 Silicon Chip
lay out the cable and the 25-pin male
sub-D connector in front of you. Find
pin 1 of the IDC connector and solder
the other end of the wire to pin 18 of
the sub-D connector. Work through
pins 2-8 of the 10-pin IDC connector
and solder in all eight connections to
the sub-D connector as outlined in
Table 2 above.
Remember that pin 2 of the IDC
header is strand three of the ribbon
cable, pin 3 is strand five, pin 4 is
strand seven, etc. Finally, fit the
sub-D cover onto the 25-pin connector to relieve the strain on the solder
connections.
Does it work?
Connect the EPROM emulator to
the Southern Cross computer and to
your PC and power both systems up.
A new PC board manufacturing
service has been set up to meet the
demand for small volumes of quality
double sided, through hole plated
boards.
By adopting the latest disposable
photo tooling techniques, Don Alan
has managed to almost eliminate
tooling costs. The resulting prices will challenge bread boarding
techniques for prototypes and one
off manufacturing. Don claims that
prices will range from a quarter of
the usual price of other PC board
manufacturers.
All PC boards are 1.6mm fibreglass,
double sided, through hole plated,
35µm copper (1 oz), solder resist and
component overlayed. Non rectangular and internal profiles and cut outs
Type ‘em scmv1_2.hex’ on the PC
keyboard. The Data LED should light
up on the emulator for about second,
then the Ready LED should turn on,
the buzzer should sound and ‘2000’
should appear in the Address displays
on the Southern Cross (you may have
to press the Reset button).
If this is OK, enter ‘em 3digit.hex’.
Go to Address 1800 and press Function
0. A 3-digit count should be displayed
on the right three displays. It should
be possible to increase or decrease
the readout with the “+” and “-” keys
respectively.
All the procedures and software for
the emulator are supplied on a floppy
disc which comes with the kit. The
designers suggest that the emulator
software be used in conjunction with
a program such as Norton Commander
for most efficient creation of code for
SC
the Southern Cross.
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