MAGAZINE SOBRE HISTÒRIA (Iniciat com AUCA satírica el 1960.. en edició de M. Capdevila a la classe de F.E.N. )
"La història l'escriu qui guanya".. així.. "El poble que no coneix la seva història... es veurà obligat a repetir-la.."
|06-09-2018 (90 lectures)|
- 1 x CPU XC6800B 8-bit microprocessor. In the early days, Motorola used the prefix XC, instead of MC, for engineering prototypes. This chip has a 1 MHz max clock frequency and- as the others in this board- is housed in a ceramic DIP, with a gold top and gold pins.
- 7 x MCM6810L 128-byte static RAM. The first six RAM, addresses from 0 to 027F hex, are the RAM program memories. The user has the huge amount of 640 bytes for storing his program code. Yes, I'm talking about 640 bytes, not Gbytes, not Mbytes and not even kbytes¬†! Don't forget, we were in 1975.
The 7th MCM6810L (address at A000 hex) is used by the MIKBUG control program as a temporary storage and stack area.
-¬†1 x MCM6830L7. This is a 1024x8 mask-programed ROM, located at E000 hex. Two resident control programs, MIKBUG and MINIBUG are firmwares allowing the loading, debugging, and controlling of the user programs.
- 2 x XC6820 Peripheral Interface Adapters (PIA). XC prefix for engineering prototypes. This device is capable of interfacing the MPU to peripherals through two 8-bit bidirectional parallel ports and four control lines.
- 1 x MC6850L Asynchronous Communication Interface Adapter (ACIA). Used to interface the MC6800 to asynchronous serial devices.
Additional components are used for interfacing and/or controlling these chips : CPU and UART clock generation, connection to the external world, etc.
The board needs 3 power supplies : +5 V (1 A) for the M6800 chips and the logic glue, +12 and -12 V (#¬† 100 mA) for the RS232 interface. RS232 rates are 110 or 300 Bauds but only 110 Bauds is available on this module. In 1975, the 110 Bds ASR33 Teletype¬ģ, with automatic reader and punch options, was the most frequently used terminal (20 mA loop current or RS232 V24).
The schematic shows that this speed is defined by a RC network connected to a MC14536 chip used as a timer : I try to adjust R (a 47kOhms potentiometer) to get a 9 ms half-period on TP4, as explained in the manual. No success !
Before conducting more experiments, I put the evaluation module in a box to protect it against dust and shocks.
However, I choose to play the game as I did 40 years ago and to write machine code the old way. Here is a copy of the paper sheet of one of my recently hand-assembled small program displaying "HELLO WORLD" :
This program makes use of the PDATA1 MIKBUG routine to display the ASCII string and of the CTRL routine to give control back to MIKBUG at the end.The MIKBUG firmware enables the user to perform the following functions :