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MAL-4: Microcontroller Aid for Learning; Pt.2 This month, we publish the complete circuit diagram of the MAL-4 & describe how it all works. It's based on a Motorola 68HC705CB microcontroller. By BARRY ROZEMA As noted last month, the heart of the MAL-4 is the Motorola MC68HC705C8 Microcontroller Unit (MCU). It has the following internal "peripheral" devices: EPROM (7.6K) , RAM (304 bytes), ROM (240 bytes), bootstrap, crystal oscillator & divider, watchdog timer, interrupt timer/coun58 SILICON CHIP ter, synchronous & asynchronous .serial interfaces, three 8-bit ports and one 7-bit input only port. A 2MHz crystal (XTAL1) is connected to the oscillator pins (38 & 39) of the MCU. The MCU divides the crystal frequency by two, giving an internal clock rate of 1MHz or lµs. This means that if an instruction takes five clock cycles to complete, you know how much time it takes (5 x lµs = 5µs). The MC68HC705C8 is a true "single chip microcontroller" and therefore provides no access to the internal busses. Instead, it has four input/output p9rts. The four ports are called (for want of better names) Port A, Port B, Port C & Port D. Ports A, B & Care 8bit bidirectional ports; ie, any bit(s) can be used as an input or output. Port D is a 7-bit input only port (bit 6 is missing). On the MAL-4, the ports have logic switches or logic monitors connected to them. Ports A and D each have eight data switches connected, while ports B and C each have eight LED data monitors. Port A is used as a data bus and has a number of devices connected to it. They are the liquid crystal display (LCD), the hexadecimal keypad and the port A data buffer (U8, a 74LS541). Port A is configured as an input to communicate with the hex keypad and the port A data buffer. It is configured as an output to write to the display and as an input to read from the display. Port B is connected directly to the input/output socket (PLZ). The logic levels on this port are indicated by eight LEDs which are driven by octal inverting buffer U4 (74LS540). This port is configured as an output but can also be configured as an input by the .user. Port C is used as a control port. It is connected to and controls the display, the hex keypad, the port A data buffer, U8 and the loudspeaker. It has 8-bit LED data monitoring like port B, which is driven by octal inverting buffer U3 (74LS540). Port D is an input only port. It is connected to seven data switches in the form of an 8-way DIP switch (DIP SWZ). If a switch is ON, it shorts the input to ground which makes the input low (0). If the switch is OFF, the input is pulled high (1) via a l0kQ resistor (RP2) to +5V. If the appropriate switches are turned off, Port D can also be configured. as a communications port. Port D has a synchronous and asynchronous serial communications interface called the Serial Peripheral Interface (SPI) and Serial Communications Interface (SCI) respectively. The SPI is connected to a 5 or 8-pin DIN socket. This can be used to drive an IBM XT type keyboard or other synchronous serial devices. The Serial Communications Interface is connected to an RS232 line driver IC (U5, a MAX-232) and PL1. This device converts the 5V TTL signals to ±l0V RS232 levels. The MAX232 chip internally generates its own +10V and -lOV supplies to do this. Operation of the display The 16-character 2-line alphanumeric, intelligent, liquid crystal display can provide the full range of ASCII characters. The MAL-4 talks to the display via port A in an 8-bit parallel format. The control lines, R/W, Register Select and Enable are fed from port C. . The display can be disabled by a link (LNKl). Position 1 enables the display by connecting the enable (E) signal to port C bit 4 (PC4). Position 2 disables the display by disconnecting the E signal and ties the E pin on the display low (0V) via the lOkQ pulldown resistor (R28). VRl is a contrast (viewing angle) control (VRl) which places a DC bias on the VO pin of the display. This enables you to adjust the display to suit your particular viewing angle. Operation of the hex keypad The keypad is an 6 x 4, x-y matrix or row/column type. The column is 4bit and it is driven by port C via a 1-of4 decoder (U6a, 74LS139). This pulls each column low in turn. The row is 8-bit and is read by port A via an octal data buffer (U7, a>74LS541). Each of the eight rows are pulled high via a l0kQ resistor (RP3). If no key is pressed, the row will read high (1) for each of the four column scans. If a key is pressed, a row will read a low (0) on a given column scan. The MCU knows which key is pressed by reading the row/column reference. The keypad circuit can be disabled by a link (LNKZ). Position 1 enables the keypad circuit by plac.i ng a low (0) on the enable pins ofU6 and U7. Position 2 disables the keypad circuit by placing a high (1) on the enable pins via a lOkQ pull up resistor (RP3). Operation of port A Port A is an 8-bit input only port connected to the input/output socket (PL2) and to eight data switches in the form of an 8-way DIP switch (DIP SWl). Its operation is the same as the switches on port D. It is read by the Fig.2 (next page): the MAL-4 circuit is built around the MC68HC705CB Microcontroller Unit. It features synchronous & asynchronous serial interfaces and four 8-bit input/output ports. Ports A, B & C are 8-bit bidirectional ports (ie, any bit(s) can be used as an input or output), while Port Dis a 7-bit input only port (bit 6 is missing). PARTS LIST 1 MAL-4 PC board 1 2MHz crystal 1 24-button keypad 2 PC mounting keyswitches 2 8-way DIP switches 4 3AG PC fuse clips 2 3AG 1A fuses 1 60 x 32 x 30mm TO-220 heatsink (DSE Cat. H-3401) 1 8-way 0.2-inch PC-mount screw connector 1 40-pin DIP socket 1 28-pin DIP socket 4 20-pin DIP socket 4 16-pin DIP socket 1 16-pin header plug 1 26-pin header plug 3 3-pin 0.1-inch SIL PCB plug 3 0.1-inch shorting links (to suit above plugs) 1 plug -to suit display 1 socket to suit display 1 5-pin DIN right-angle PCB socket Semiconductors 1 MC68HC705C8S (EPROM version) with monitor program by E.S.D. 1 Seiko M1632 16-character 2line alphanumeric LCD 2 74LS540 octal inverting buffers 2 74LS541 octal buffers 1 74LS139 dual 1-of-4 decoder 1 7805 5V regulator 1 MAX232 line driver 3 BC108, BC548 transistors 1 WO4 1.SA bridge rectifier 4 1N4001 diodes 1 1N914 diodes 17 3mm LEDS 1 3mm high brightness LED Capacitors 1 2200µF 16VW electrolytic 1 1µF 16VW tantalum 11 10µF 16VW tantalum 4 0.1 µF ceramic or monolithic 2 27pF disc ceramic Resistors (0.25W, 1%) 1 10MQ 1 2.7kQ 6 10kQ 17 150Q 1 4.7kQ 1 10Q 3 10kn x 9 SIL resistor packs 2 4.7kQ PC mount trimpots Miscellaneous 3 3mm x 10mm-long machine screws, 3 3mm nuts, 3 3mm ID spring/antishake washers DECEMBER 1992 59 ,! Ii RESET KEY5 C10 1 r +5V !• R22 10k -- R2 10k 02 8C548 C ~ RESET PAO Cl RESET/ S3 PA1 PA2 PA3 ~E PA4 PAS ':" 35 TCMP 37 TCAP 39 j_ I 'f C3 .LxTAL1 27pf 2MHz ':" · C4 PA8 TCMP PA7 TCAP PBO OSC1 PB1 R1 10M P82 38 .l. PB3 OSC2 P84 U2 88HC705C8 27pf + PBS PB8 2 IRQ PB7 IRQ VDD PCO +SY POO lu1 IRQ KEYi ---;;;;-; PDO PD1 R2 10k _,_ P02 I) 1 01 R21 10 -- LNK3 -~ :f~> 2 C 0 .1+ ':" I) R27 10k 29 31 P03 32 PD4 33 PD5 34 P07 38 PC1 PC2 PD2 PC3 PD3 PC4 PD4 PCS PD5 PCS PD7 PC7 +SV I 40 1 .... ar.::i) 04 ( 1N914 • YOO I RESET PAO 18 10 PA1 PAI 17 9 PA2 PA2 16 8 PA3 PA3 15 7 PA4 PA4 14 +5V 8 PAS 5 PAS PAS 4 PA7 12 PBO PBO 11 13 PB1, P81 12 14 PB2 PB2 13 15 PB3 PB3 15 16 PB4I 17 PBS 18 PBB 19 PB7 C,. PB4 18 PBS 17 PB8 18 Al 9 PA1 D2 8 A2 A3 7 PA2 A4 8 PA4 03 D4 24 28 PC2 PC2 21 PC3 23 24 PC4 I PC4 2 23 PCS, PC7 22 3 01 02 02 03 03 08 U1 A8 19 4 PA2' 5 PA3' E2 Ei~PIN2 RP2 -!!o PA3 +SV t 20 PA2 13 A8 I PA4 A10 PAS A11 PA8 A12 I ce PA7 PC2 9 ROWO 08 D8 07 D7 8 ROW1 7 ROW2 08 8 U7 D5 5 15 74LS641 04 04 4 18 D3 03 17 3 02 D2 2 18 01 01 19 1 PA3 14 A9 OE 3 PAI' 04 AS ,-5__~5.., D5 08 05 ROW3 ROW4 ROW5 ROWS ROW7 E2 Ei -t +o VPP E PC3 r-- PA1 12 PC1 PC7 I AO 01 PA7 25 ,PCO .- PCB 00 ~ D7 2764 A7 3 PCOI 22 PAO PAO 11 PC1 I 21 PA7 10 PAS 27 PC3 r PAS 27 2 PAO' 01 04 6 PA4' ua QS 74LS541 OS 13 7 PAS' 08 08 12 8 PA&' 07 07 11 08 08 ~ 4 28 25 ,,...--- t2, 11 PAO -:1:10 .,!30 ':" ... +SY R28 2.7k R3 10k VDD D1 1N4004 GD AC VPP +12V +5V GND +8 SPKR -- 0- - ...... I) 26: 10 0 R 2200i - 4 RS D3 R/W 04 3 05 D8 E 11 PCS 10 PC8 9 LNK1 1,-- GND -YLED -!!3 R20 10k ~8 0 10 ~ GND C15 -:- DS R28 4.7k +5V C 03 BC548 8 PC7 - SILICON CHIP - VOLUME VR2 1k -0 - +5V 10 LED1 ~ POWER ·• ~ 03( 1N4004 rt 2 ':" ~~""h C18 ~ I■ ~ 1::1\ \;J '-::,/ 1N4004 BATTERY WARNING ~ R24 1500 VDD Cl 1 ■ jt IGO '-- PC4 +SV 120 PCO 2 PC1 3 PC2 4 PC3 5 PC4 6 PCS • 7 ·-:- LED2 r.:'\ EOc VIEWED FROM BELOW ':" U9 0 F2 ":" ~ E 60 5 PA4 D1 LCD 02 M1832 B CONTRAST VR1 1k \:;I POWER S1 ~,.:. - --- PA3 VDO +VLED 12 VO 17:\ POWER 0- 8 D2 1N~004 • -- PA2 DO ~ D7 8R1 AC 7 ...~ l coNNECTOR 8 PAI PAS I) VPP S2 PAO ~ 15 114 PC8 8 --.fQL! 0.1+ MAL-4 MICROCONTROLLER vcc D1 01 02 02 03 18 D6 .... RB 08 06 07 D7 DL _ E1 E2 .... 14 12 LED9 K~A V LED& K~A R8 R9 LEDS K~A R7 .... V. .... l2 RIO .... Q8 11 R11 ~10 V,_ V..KLED7 ~A LE08 V K~A .... 04 05 RS 18 03 U3 74LS540 .... 17 15 D4 8x1500 LE010 R4 K ~ A .... V!:j LED4 K~A V LEDS K~A \D PORT C LED MONITORS PCO PC1 PC2 PC3 PC4 PCS PCB PC7 +SV +SY 20 PBO ·- - -- 01 Q1 PB1 · - - - - 02 02 PBO 19 RP1 10k P81 Q3 18 PB2 2 TCAP PB3 · - - - - 04 +SY RP3 10k 1 PB4 6 OS PBS 7 i 2 i : : 3 4 s 7 6 8 PB& 8 9 10 U4 74LSS40 PB7 9 05 08 Q6 07 07 08 E1 E2 08 14 R18 13 R1!. 12 R18 11 i R19 w 7 8 9 10 PAO' PA1' PA3' PB4 LE013 K~ A PA4' w PBS w b PA6' PB6 LE011 K~ A +SV PAS' PA7' 1 P87 PORT B LEO MONITORS ~ 19 6 PA2' LE012 K~ A w 5 4 P83 LE014 K~ A w 3 2 4 3 s 7 8 18 15 14 13 12 11 10 9 + LNK2 I 0 -- I 2 E A B vo 4 8 s r+ 7 ~ ...... C1+ C11 : : 10 _ C1· 16 PIN HEADER (25 PIN RS232) 2 y. 8 C2+ LINKS us ce C c12 .I. MAX232 1o u 10 ~ C214 TX DATA P01/TOO 11 T11 T10 POO/RD1 12 13 RX DATA R10 R11 GNO §"'"' 0 0 11 RO W7 10 ROWS 9 ROWS 8 ROW4 7 RO W3 8 RO W2 5 ROW1 4 ROWO 2 0 0 3 0 1 08 10 18 07 OF 17 20 KEY2 1F KEY1 1E KEY4 10 KEY3 08 OE 18 05 00 15 04 oc 14 1C 03 0B 13 18 02 OA 12 1A 01 09 11 19 PIN19 U8 -P07 4 8 7 8 9 P05 22 0 TCMP - 250 IRQ -~- 10 P03 PD4 260 t POO 23 _ P01 24 -= :~ -f I I "' ~ 210 TCAP - P04 P03 - w 0 - : 3 (2) s - PB6 18 = PB7 20 ':: : 3 "" 0 9 (S) . b 1(1) ~ 13 (7) 2 8::. : S (3) RP2 10k 0 PB1 PB4 14 _ PBS 18 = 1 0 0.. 15 (B) 11 (6) +SY ... ..."' ...... 6_ PB3 12 RESET 0 PBO PB2 10 = 0 7 (4) +5 3 N J1a YCC V+ 3 4 Y1 Y2 Y3 13= t C8 10 L _ 8 us 74LS139 PA4' +SV 1 18 PA3' - 2 T 1 3 9- 11_ PA7' 19_ , 11 - - PA2' PAS' 1s: PA6' 17 _ PORT A DIP SWITCH ,-- 1: PA1' \\\ 1\\\\ SW1 L PAO' 8 SPI INTERFAC E 5-PIN DIN P02 P01 8x4 KEYPAD (32 KEY) POO 16 15 14 13 12 11 SW2 10 9 \\\ \\\\ 1 2 3 4 5 8 7 8 -,r PORT O DIP SWITCH D ECEMBE R 1992 61 MAL-4: Microcontroller Aid For Learning MCU via an octal data buffer (U8, a 74LS541). The MAL-4 monitor program allows port A to function as an input port under a user program or it can be disabled by switch 6 on DIP SWZ. If the switch is in the ON position, the octal data buffer (U8) is enabled. The loudspeaker is driven by bit 7 of port C via NPN transistor Q3. This is a BC108 (BC548) configured as an emitter follower. The level of signal fed to the transistor is set by volume control pot VRZ. R28 limits the maximum volume level and can be reduced if a higher volume is required. The monitor program generates a series of highs (1) and lows (0) to generate tones from the speaker. Power supply The MAL-4 can be fed from a 12V Hear what the It runs in the family. test panel had to say First Concert VII voted say about Concert II: 'Loudspeaker of The "On audition it didn 't Year'. Now the smaller take long to establish model Concert II that the Jamo was winning hands down something special. in.a group test with 8 The speaker simply other loudspeakers sounded more transin the UK magazine parent and revealing "High Fidelity". than the other speakThe conclusion of ers in the test.... They the test was: "The imaged better.... A speaker that resolved deep, tangible bass the problem was the and crystalline mid dark horse Jamo. Very and treble clarity.... much an unknown Imaging was virtually quantity in the UK, it holographic... " was nothing less than a With 24 years exrevelation when put to The test winner perience having prothe test. It was the one duced more than 10 speaker here with million loudspeakers, genuine grip and grace 2-way bass reflex Jamo is today and, as such, ended up System: Woofer: 1 70mm Polypropylene Europe's preferred the overall winner. " Tweeter: 25mm sofl dome loudspeaker brand. When a Danish Power Handling: 80 watts RMS Timber Finishes: Walnut and Mahogany To experience _ loudspeaker is the RRP: !Timber finish) $1190 pair why Jamo is winning preferred choice in (Black Ltd. Edition) $ 990 pair time and time again, the UK over such brands as B&W, Mission, Heybrook, call into your nearest authorized Jama specialist or contact Scan Castle and Tannoy, it must be of outstanding design, And this is Audio for more information and exactly·what Jamo's Concert II is. the name of your nearest dealer. CONCERT II uamo AWARD WINNING LOUDSPEAKERS SCAN AUDIO, 52 Crown St, Richmond VIC 3121. Phone: (03)429 2199. Fax (03)429 9309 62 SILICON CHIP DC plugpack or a 12V battery. Alternatively, a 9V AC supply can be used. It is full wave rectified by bridge rectifier BRl and filtered by a ZZ00µF electrolytic capacitor (C13). This feeds U9, a 7805 3-terminal regulator to produce a +5V supply which feeds the ICs on the board. This +5V supply also provides the Voo rail for the microcontroller via diode D3. There is provision for a battery backup supply for the RAM. Normally supplied by three AA cells in series (off board), the line feeds the Voo rail via diode D5 and LED 2, when the +5V rail falls. LED 2 is a battery warning indicator. It is a high brightness type and indicates when a current of more than lmA is drawn from the battery. This can occur if the MCU is not shut down before the power is removed. The MCU current under shutdown (STOP) conditions is in the order of a few microamps. Reset circuit The MCU requires its pin 1 to be pulled low for the reset condition to occur. The reset can come from four places: reset switch (S3), pushbutton reset (KEY5), at "power on", or via the input/output plug (PLZ). The reset switch (S3) works simply by pulling the reset pin to 0V. It is intended to be used when the MAL-4 is used as a programmer. Alternatively, the pushbutton reset (KEY5) turns on transistor (QZ) and this pulls the reset pin low. The power-on reset circuit works as follows. Capacitor Cl0 is discharged via diode D4 when the +5V rail falls. When power is applied, ClO is charged via RZZ and the base of transistor QZ. While the capacitor is charging, QZ is switched on and pulls the reset pin low. When Cl0 is fully charged, QZ turns off and the MCU resumes normal operation. Interrupt request The escape or Interrupt ReQuest (IRQ) circuit supplies the MCU with a low (0) on pin 2. The IRQ comes from pushbutton KEY6. This turns on transistor Ql via resistor RZl and pulls pin 2 of the MCU low. · Both the reset and the IRQ circuit prevent the MCU from being reset when there is no power applied to the MAL-4. This is necessary otherwise it could be taken out of the shutdown The assembly of the MAL-4 microcontroller is straightforward as all the parts are mounted on a double-sided PC board with plated-through holes. A kit of parts will be available from the author (details next month). mode (STOP) if the reset or IRQ buttons are pressed and thereby cause excessive battery consumption. Link LNK3 in the IRQ circuit provides the IRQ pin on the MCU with a pull-up voltage of +5V in position 1 or +9V in position 2. Position 1 operates the monitor program while position 2 operates the Boot loading program. Programmer mode If links LNK1 , LNK2 and LNK3 are placed in position 2 and the 8-way DIP switch (DIP SW2) is set correctly, all the MAL-4 peripherals are disabled (display, keypad, monitor EPROM and port A buffer) and the unit becomes a programmer. Note: last month's overview of the MAL-4 may lead readers to believe that the unit can program EPROMs. This is incorrect. At this time, the MAL-4 can only program the EPROM inside the MCU. The steps involved in programming the internal EPROM are set out in the Motorola MC68HC705C8 Technical Summary (BR594/ D). Programming can be done in the following ways: (1). Program and verify internal EPROM from the 8K EPROM (U1) (2). Verify interna"i EPROM contents from 8K EPROM (U1) (3). Secure internal EPROM (4). Load and run program in RAM via RS232 (5). Dump internal EPROM contents via RS232 (6). Run program in RAM When LNK3 is placed in position 2, the MCU is placed into the bootstrap program mode. This mode uses the internal bootstrap ROM. DIP sw 2 selects the programming mode. S1, S2 and S3 are used to switch the power (Vpp) and take the MCU out of reset to enter the programming mode. The 8K EPROM (U1, 2764) is used as the program source. Its data is loaded via port B while the address locations are incremented via ports A and C. Data can be sent to the RAM or from the internal EPROM via the RS232 interface to a PC. LEDs PC5 (LED 5) and PC6 (LED 4) indicate that the program is verified and that the MCU is programming. Next month, we will present the full constructional details for the MAL-4 microcontroller. SC We have over 1,000 different printed circuit boards and screen printed front panels for kitsets from EA, ETI, AEM, HE and Silicon Chip. On special this month only for half normal price! For a complete list of available PCBs and front panels, their date of issue and price, simply send your name, address and stamped self addressed envelope. Note:Duetocopyrightlaws we cannot supply copies of magazine articles. These are available from libraries or the magazine companies (by arrangement) ALL ELECTRONIC COMPONENTS 118-122 Lonsdale St. M elbourne 3000. Ph: (03) 662 3506. Fax:(03)6633822. ~ -~- - - - - - - - - - - - I I ;:.:N.=.am:..=.e_ _ _ _ _ _ _ _ __ I I I -----------I I Address I -----------I I -----------I I Postcode I -----------L ____________ _ .J D E CEMB ER 1992 63