The Microlog MC52 is an STD bus single board computer that uses an Intel 8052AH-BASIC microcontroller. This microcontroller includes a masked ROM containing a BASIC interpreter.
I have not been able to discover much about Microlog, which is a shame because they were a local Adelaide company.
Based on IC date codes, the board was manufactured around 1988. It includes 32 of static RAM, an EPROM socket, parallel port, programmable interval timer, and a serial port.
User interaction is via a terminal connected to the serial port. After power-up, the operator has to type a couple of spaces so that the baud rate can be detected.
I have no manual for this board, but i expect that it is similar to one of the configurations described in the Intel MCS BASIC-52 User’s Manual, eg the one in Figure 2A.
It clearly has some differences, including the STD interface and a P8255 Peripheral Interface – probably connected to the 40 pin connector on the front of the card.
One of the unusual features of this BASIC is that the interpreter allows programs to be stored in and executed from EPROM. Looking at the board, the programming voltage seems to come from an external supply.
I thought this card may be quite handy for testing some of the STD cards that i have, but i will need to work a few things out first, including addresses. The STD bus has an I/O space, but i don’t think the 8052 has such a thing, so i’m guessing it’s mapped into memory somewhere. So i did a bit of buzzing out ….
I found that the top 3 address lines are decoded into 8k chip selects. The bottom 4 (0,1,2,3) are used for the 8k static RAM chips (HM6264). The next two (4,5) are used for the EPROM so it can be a maximum of 16k ie 27C128. The next one (6) is used to enable the second decoder. The last one (1) selects the STD bus I/O space. There doesn’t appear to be a mechanism to access the STD memory space.
| 0000-7FFF | Static RAM |
| 8000-BFFF | EPROM |
| C000-DFFF | Second decoder |
| E000-FFFF | STD I/O |
| C000-C0FF | 8255 Programmable Peripheral Interface |
| C400-C4FF | 8253 Programmable Interval Timer |
The second decode breaks C000 to C7FF into 8 x 256 byte spaces. These are mirrored in the remaining space.
External memory is accessed from BASIC using XBY “function”. I tried the Pro-Log 7601 Input/Output Card and was able to read and write the registers at 00-03 using XBY(0E000H+i).
I also briefly tried the 7301 Serial Card which registers at C0 and C1 using XBY(0E0C0H+i). That also responded as expected.
The MC52 is definitely useful for testing I/O boards. Memory cards are a different problem.