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This photo shows a Z80 SBC thats a single board controller or computer with upto 32Kb of Eprom
for the control program and data and 32Kb of RAM, two 8255 I/O chips each giving 24 control lines in 3
8 bit ports A, B and C. It measures 8"x4.5" and has been used to control home-made robots, stepper motors,
a data logger for a weather-station, etc. It is produced by the same company that produced the Interak computer,
and indeed can be used in that computer as a general purpose input/output interfacing card... |
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A typical controller board needs! a CPU Z80 or otherwise, an Eprom chip to hold the controlling program or
code, RAM memory chip(s) for data storage and progam variables, an I/O chip for interfacing to the outside world,
and a few TTL logic chips for address decoding, etc. Not forgetting resistors, capacitors and the odd diode to glue
it all together |
| A microcontroller, in a conventional controller system using
a CPU (Z80,6502, etc) the CPU would also require extra devices to provide memory, timing, I/O ports etc.
In a microcontroller CPU, memory, timers, I/O ports and sometimes even A/D converters are all brought together
in one device, a microcontroller. The Arizona-Microchip PIC series are so easy to program, and
need very few components to make a working system..... |
| Here is a small (2"x2.5") home-made controller based on Microchip's
PIC-16F84 (or 16C84) microcontroller while this is not so powerful in some ways as a Z80, it has many benifits, size, low power,
low component count, a timer and pre-scaler. it's own built-in system clock can run at upto 10MHz. It has both programmable EEprom
and data memory, and includes 68 general purpose registers, Interupts, 13 I/O lines consisting
of port A D0-D4, port B D0-D7 all capable of sourcing or sinking 25mA to directly drive LED's etc..
There are only 35 istructions, so much easier to learn and remember than 158. Will go to sleep (save power) when
not active, wake-up on a key press, interupt, etc... This and some other PIC's can be reprogrammed over and over again! |
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So just what do you need to build a microcontroller?? not much a PIC 16F84 chip, a PCB or piece of
Vero board, 2x39pF capacitors, 1x10-100uF cap, 1x 0.1uF cap. A crystal upto 10MHz, 4MHz seems very popular!
or this can be replaced by a small cap and resistor if a precise clock is not required, this is
also useful if you need a slow clock speed. Power-on reset may be required this will need a 1-2.2uF cap and a 10k resistor.
You now have a working controller, you can now program it to read switches, light up LEDS, drive relays and LCD displays, etc
and generally control and time things. And all of this will still give you change from £10, building a simple programmer will cost you
about the same. |
The controller shown has two sets of pin headers, the larger for all I/O, power, and control signals. The smaller is a direct pin compatable
connector for intelligent LCD modules, allowing direct plug-in or ribbon connection to these. Want to know more about PIC microcontrollers.
you can call Microchip on 0118-9215858 or e-mail Dr Mac at Drmac@microchip.com or visit their website
at www.microchip.com Don't forget to mention you read it on Mel's page
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