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MAL-4: Microcontroller Aid for Learning Here is a microcontroller design which can be used to learn programming and computer c~ntrol. It features the Motorola 68HC705CB microcontroller and has serial and parallel ports. You can program it via its own hexadecimal keyboard or via a standard IBM computer keyboard. 34 SILICON CHIP By Barry Rozema A single chip microcomputer, as the name implies, is a microcomputer in a single chip package. This means that all the building blocks of the microcomputer are in the one integrated circuit. The building blocks for most computers are the central processing unit (CPU), memory (RAM & ROM), parallel and serial input/output (I/0) ports, address decoding, clock, interrupt timer and watchdog timer. Single chip microcomputers or microcontrollers have found a very important niche in the computer industry. Due to their size and low cost, they are very effective when used for control applications such as in washing machines, microwave ovens, VCRs and burglar alarms. The microcontroller used in this project is the Motorola MC68HC705C8. It is an 8 bit microcontroller with a user programmable EPROM inst~ad of mask programmable ROM. This makes prototyping and development a reasonably easy task. Why use the MC68HC705C8? The main reasons were cost and availability plus the fact that I like Motorola's "easy to understand" data sheets and manuals. And why design and build a single chip microcontroller learning aid? I realised when I first started programming the 68 705 that it would be handy to run some small test programs to familiarise myself with the devicA. After some enquiries, I discovered that there are some development tools for the 68705 but the prices were out of my league. So the idea of designing a cheap single chip learning aid was born. Main Features • Processor - Motorola MC68HC705C8S. • Clock speed - 2MHz/2 (1 MHz internal clock). • Display - 2-l ine by 16-character alphanumeric LCD. • Keyboard - Hex keypad with option for different types. • Power supply - either 9V AC or 12V DC. • Monitor - resides in EPROM (5Kb) and includes disassembler. • Two modes - MAL-4 or single chip monitor mode. • Emulates the Motorola M68HC05PGMR programming board. • Battery backup of RAM. • Ports: A - 8-bit input port with 8-way DIP switch. B - 8-bit outpuVinput port with 8 LEDS. C - 8-bit control port with 8 LEDS. D - 7-bit input only port with 8-way DIP switch or asynchronous (RS232) and synchronous (IBM keyboard) . • Ease of construction • Stand alon e operation • Possible u se as a controller The MC68HC 70 5C8S microc ontroller is a recent addition to th e Motorola 6805 family and is similar to the 68 705P3 processor featured in the Sprinkler Controller published in the July 1992 issue and the Burglar Alarm publish ed in th e September & October 1992 issues of SILICON CHIP. The " HC " des ign ation of the 68HC705C8 signifies that it is a high speed CMOS version (ie, high speed, low power). It is one of m any versions of this chip so that once you have learnt h ow to program it , you w ill have no trouble with the other versions and indeed you will have a good grounding in programming any microprocessor. Block diagram The block diagram of Fig.1 shows MAL-4 Entitled "Microcontroller Aid for Learning, Version 4.03" or MAL-4, for short, this project is the fourth in a series which have been designed primarily as a learning tool for TAFE colleges. I paid close attention to the following points: • Low cost • Current processor technology • Simple design The MAL-4 uses a 2-line alphanumeric readout which plugs into a socket on the PC board. It is an intelligent unit which accepts ASCII code. NOVEMBER 1992 35 TABLE 1: MAL-4 MEMORY MAP Input/Output 32 Bytes· $00 Port A Data Register $01 Port B Data Register $0020 - $002F Unused 16 Bytes $02 Port C Data Register M.A.L. Zero Page Ram 144 Bytes $03 Port D Input Register $0030 - $00BF $04 Port A Data Direction Register $00C0 - $00DF M.A.L. Scratch Pad 32 Bytes $05 Port B Data Direction Register $06 Port C Data Direction Register $00E0 - $GOFF System Stack 32 Bytes $07 Unused $08 Unused $0100 - $01 5F M.A.L. Page 1 RAM 96 Bytes $0000 - $001 F Unused Serial Peripheral Control Register $0B Serial Peripheral Status Register $0160 - $12FF M.A.L. Monitor EPROM 4512 Bytes $1300 - $1 EFF Spare User EPROM 3072 Bytes $DC Serial Peripheral Data 1/0 Register $OD Serial Communications Baud Rate Register $1 FOO - $1 FOE Bootstrap ROM 223 Bytes $OE Serial Communications Control Register 1 $OF Serial Communications Control Register 2 $1FDF Option Register $10 Serial Communications Status Register $1FE0 - $ 1FEF Bootstrap ROM Vectors 16 Bytes $11 Serial Communications Data Register $12 Timer Control Register $1 FF0 - $1FF3 Unused 4 Bytes $13 Timer Status Register $1 FF4 - $1 FFF M.A.L. EPROM Vectors 12 Bytes $14 Input Capture High Register most of the significant features of the MAL-4. It leaves out essentials like the power supply, speaker driver and even an external EPROM which the unit can be used to program. The 68HC705C8 has 24 bidirectional input/output (1/0) lines and 7 input-only lines. These are arranged as three 8-bit 1/0 ports (A, B & C) while the 7 input-only lines are port D. Interestingly, while these 7 lines are specified by Motorola as input only, the first line (PD0) is also used as an output line, to provide the Tx line for RS-232 serial communications (via a MAX232 chip on the board). Port A is used to drive the 2-line liquid crystal display, along with a couple of the lines from port C. The liquid crystal display is an intelligent device and it accepts ASCII characters on its parallel data lines. Ports B and C drive a bunch of LEDs which show the state of the lines. One data line of port C also 36 $09 $0A SILICON CHIP $15 Input Capture Low Register $16 Output Compare High Register $17 Output Compare Low Register $18 Counter High Register $19 Counter Low Register $1A Alternate Counter High Register $18 Alternate Counter Low Register $1C Program Register $10 COP Reset Register $1E COP Control Register $1F Unused drives the speaker to provide the occasional beep or two, to acknowledge that the micro is receiving or feeding out data. The 16-button hexadecimal keyboard is connected to ports A and C via row and column driver ICs. Port A also provides the external parallel port. An IBM keyboard can be connected to the unit and it drives four of the lines of port D. DIP switches are also provided for data input to port A and port D. Two pushbuttons are provided for "Interrupt Request" (IRQ) and "reset" . All of _the above features can be gleaned by examining the block diagram of Fig.1 but let's face it, that will not really tell you much about how the micro works. That understanding will come gradually as you learn more about programming the device and DIPSW1 PORT-A ,I, 1,1\' l ll :\' 1/0 CONNECTOR PL2 I, I l l PORT-A PORT•B LCD J I ...< a.. .,J PORT-A INPUT BUFFER ' PC3 ,, A BUS -. E RS R/W 8-BIT DATA ca.. "'a..< .,J < a.. .,J < a.. "'< ca.. <O < a.. a.. ,, • "' a.. a.. 0 <O 0 a.. .,J ( .,J [ 0 ,, ,, , " PA7 PA6 PAS ,, < PA4 PORT-B LED MONITORS .:. ~ PAS a.. PA2 l. PA1 PAO XTAL1 2MHz [ PB7 OSC1 Ir r PBS OSC2 m P84 ,J ~ P83 ,J PB2 .,J .:. a.. RESET T P81 .,J PBO ~ PORT•C LED MONITORS PC7 .,J PC6 ,J .:. IRQ PC2 .,J PC1 ,J PCO .,J 'I 0 0 ,1, I, I, I,~\' I l I r .,J " .:. ~ PD3 a.. PD2 .,J PD1 .,J PDO ,, TXIPD1 MAX232 ]PDO RX 1 TX .I DATA IIDATA RX RS232 PLUG 8 U6 74LS139 COLUMN DRIVER II .A D BUS a PD4 ' ' "'00.. :::, "' "' < PD5 PD4 IBM PD3 KEYBOARD SOCKET PD2 8x4 X-Y KEYPAD UP TO 32 KEYS U7 74LS541 KEYPAD ROW BUFFER I Fig.1: this block diagram shows the main features of the MAL-4 microcontroller board. It has three 8-bit input/output ports (A, B, & C), while Port D has seven input lines. Two of these lines do double duty as the RS232 serial port. Data entry can be via the on-board hex keypad or via a standard IBM keyboard. how it handles data to and from its ports. Physically, the MAL-4 is constructed on a double-sided PC board measuring 223 x 153mm. It has a zero insertion force (ZIF) socket to allow an external EPROM to be used or programmed. It has a hex keyboard as u 0.. A ~\ PD7 PD5 .... IL .,J T ~ DIPSW2 PORT-D ~ PC3 a.. l C BUS r u PC4 Ir SPEAKER ,, PCS KEY6 ESCAPE ~ PB6 U2 MCUHC705C8 MCU KEYS RESET B BUS _,, already mentioned. The board is used free-standing and it only requires the connection of a 12V AC or DC plugpack to have it up and running. As a point of interest, the MAL-4 board also emulates all functions of the Motorola M68HC05PGMR "Programmer Board". The MAL-4 microcontroller board is available from the author as a complete kit and sells for $249. The address is E.S.D. Electronic System Designs, PO Box 73, Glenbrook, NSW 2773. Phone (047) 39 4039. The kit comes with a detailed assembly & operation manual which includes listings. Next month, we will continue the description of the MAL-4 board, giving the complete circuit, construction details and the parts list. SC NOVEMBER 1992 37