256 TC (Telecomputer) Technical Reference

The Microbee 256 TC is culmination of 
five years of Microbee computer development. 

The best features of previous design have been incorporated 
onto a single, four layer, printed circuit board.

1.1. Technical spec - standard.

REL : 1987

CPU : Z80 3.375MHz clock rate
RAM : 256k Dynamic RAM.
ROM : 16k Boot / Network ROM / Kernel
v1.15 13ddba203bd0b8228f748111421bad5f
v1.20 24d6682ff7603655b0cbf77be6731fb0
Character ROMs (4/8/16K)
 4K 7493a702a5b74a4d3d324bdd9c5ae41a
 8K 614654830a7252472962fc3386396e92
16K 
Main Board Revisions: 8501-3-03C 8501-3-04CR 8501-4-01 8501-4-01a 8501-4-01b
Core Board Revisions: 8342-4-03C 8342-4-01
VDU : Memory Mapped 2k Screen RAM 
      2k Colour RAM 2k Attribute RAM 
      4k Dual Font ROM Formats 
      40x24 for Videotex 
      64x16 for Basic 80x24 for CP/M. 
      Flashing (character ON/OFF)
      Inverse attribute bit 6 (LA14) (does not need PCG). 
      16k Programmable Character Generator 
       or 131,072 pixels.
VIDEO : Monochrome standard 1 volt peak to peak
	composite video with negative sync.
COLOUR : R.G.B. intensity with positive 
	 or negative sync.
KEYBOARD : Full sized 92 keys including numeric 
	   pad and 12 function keys.
DRIVE : Single 3.5 inch, double density 800k.
CASSETTE : Built-in to load and dump programs 
	   at 300 and 1200 baud.
SERIAL : RS232. Can be used to connect modems, 
	 printers and to network with other computers.
PARALLEL : 8 bit I/O fully programmable with 
	   strobe pulse for centronic printers. Connection 
	   for Star Network.
SOUND : Internal speaker with volume control 
	for BELL under CP/M.
REAL TIME CLOCK : Using the Motorola RTC 146818. 
	          Battery backed with a nicad battery.
DISK CONTROLLER : TMS2793NL Texas Instruments.
POWER SUPPLY : 10 to 12 volts at 1.5 amps. 
	       Standby current approx 700mA to 800mA. 
	       Peak current during a single 
		disk access 1200mA.
POWER SUPPLY UNITS : For monochrome use, use the 
	             Microbee M15 monitor with the internal 
	             power supply. For Colour use, use the 
		     Microbee plug pack number 111-012 
		     (10V, 1.5amps).
OPERATING TEMPERATURE : 5-45 degrees C.
OPERATING HUMIDITY : 20%-80% relative humidity.

1.2. Technical spec - options. 
(MOST OPTIONS ARE NOT SUPPORTED WITH SOFTWARE AT PRESENT)
	
VDU : Expandable from 2k to 8k. 
      Four pages of Memory mapped screen. 
      8k Screen RAM 8k Colour RAM 8k Attribute RAM 
      Character ROM expandable from 4k to 8k or 16k. 
      16k Font ROM (expansion for other languages).
GRAPHICS : Expandable from 16k to 32k. 32k 
	   Programmable Character Generator or 
	   262,144 pixels. Full 80x24 graphics.
KEYBOARD : Can use serial keyboard instead 
	   of the internal Microbee 256 TC keyboard.
DRIVE : Second 3.5 inch, double sided, 
	double density 800k drive can be added.
SERIAL : True RS232 signal can be added 
	 for negative swing.
EXPANSION : Internal 50 way Z80 bus fully 
	    buffered available for external testing and 
	    further expansion. 
	    Internal 40 way for hard disk interface which 
	    can be used with internal 3.5 inch drives.
SOUND : Internal circuit can use either the BC548 
	transistor or the LM386 op amp. Also socket 
	available for  the TI SN76489AN sound generator.

256 TC Technical Reference 1-3 Introduction