1985 - 128K SBC (Premium series) - Technical Reference
Core Board Revisions: 8342-4-03C 8342-4-01
Main Board Revisions: 8501-3-03C 8501-3-04CR 8501-4-01 8501-4-01a 8501-4-01b
ROM : 8k Boot / Network ROM / Kernel
RAM : 128k Dynamic RAM.
Programmable Character Generator (PCG) RAM: (4-16K)
CPU : Z80 3.375MHz clock rate
REL : 1985
The Premium series microbee is complete board redesign of the 'Small Business Computer' (SBC)
which put 128K of dynamic RAM (DRAM) and the floppy disk controller (only WD2793s were used)
onto the coreboard itself. This board also included provision for the addition of the
Zilog 8530 SCC chip to facilitate high speed serial transfers.
The SBC was initially released with a drive box which held two DSDD 5.25" drives (390k formatted),
later released in versions using either 5.25" or 3.5" drives.
As originally supplied, the 128K DRAM coreboard did not have a 50-way connector.
As it had the controller on-board, the cable that connected it to the drives was 34-way.
In order to allow the connection of other peripherals directly to the Z80 bus, an add-on
expansion card was released.
The Premium series motherboard tidied all of this up with a complete board redesign,
giving the following advantages over the earlier motherboard:
* provision for on-board real-time clock.
* provision for on-board sound chip,
* 40 x 24 screen format hardware to allow interface with Videotex systems.
* colour fitted standard.
* provision for a 50-way Z80 socket on the mother-board.
* provision for a -12V supply on the RS232 output socket.
* improvements in VDU access, giving a glitchless display.
* cursor control keys fitted standard.
* volume control for the speaker.
* increase in the Programmable Character Generator (PCG) RAM
from 2k to 4k-16k to allow unlimited, character based, graphics.
1.4. Technical Reference 1986 (Tech86)