Master 128
- This page is about the Master 128 and offers information about hardware features common to related machines in the Master Series. You may also have arrived looking for the Master 512, Master Turbo, Master ET or Master Compact.
- Acorn seems to have hit the nail well and truly on the head with the Master. There will no doubt still be the sniggerers laughing at the use of eight bit technology – just as they address the memory question I kicked off with. However, my answer to them would always be 'It's not what you've got, but what you can do with it', and for my money you can do a good deal more with a Master than with any other micro around in its class at the moment.
- Acorn User, 1986[1]
The British Broadcasting Corporation Master Series Microcomputer is the successor line to the Model A, Model B and Model B+ released by Acorn Computers. The base Master 128 model is an evolution of previous BBC Micro models offering various refinements over the older machines.
Contents
- 1 History
- 2 Technical specifications
- 3 Issue differences and variations
- 4 References
History
As early as 1984 Acorn were aware that the BBC Micro, powerful and successful computer though it was, required improvement to remain competitive in the market. Schools - one of Acorn's main markets - were more or less saturated with Acorn products, while in an industry that was fixated with memory capacity the BBC Model B's 32K seemed feeble in comparison to computers with double this RAM as standard, with the 128K years soon around the corner.
Acorn's initial response was the Model B+ but soon after this machine's release word that Acorn was working on a totally new kind of BBC Micro began to spread. While this new machine was popularly referred to as the 'Model C' in the Acorn press, Acorn themselves at first used the rather inappropriate codename 'Project B'. The tentative name 'Master 64' was released in 1985, with the final name being changed to reflect the computer's standard 128K of memory.
Technical specifications
Dimensions
Width: 476mm
Depth: 346mm
Height: 79mm
CPU
8-bit 65C102 running at 2MHz clock frequency
RAM
64KB main RAM
64KB sideways RAM consisting of four 16K pages
ROM
128KB onboard ROM
Contents
35K Machine Operating System with extended graphics and Terminal software
16K BBC BASIC 4
16K Edit program and text editor
13K View 3.0 word processor
16K Viewsheet spreadsheet
16K ADFS
16K 1770 DFS
Internal ROM sockets
2 x 128 or 256Kbit capability
1 x 128Kbit capability
Total sideways ROM or RAM usable at any time 256K including 96K fitted firmware
Cartridge slots
2 enhanced Acorn cartridge slots
Internal 1MHz bus uprated to 2MHz bus speed
32K ROM capacity per socket
Sound input/output
- With replacing ROM software on a standard BBC Model B being a tedious job involving considerable dismantling and risk of damage to the chips' pins, Acorn offered a more convenient solution in the form of the Master's cartridge slots. The twin slots are based on similar technology to that employed in the Electron's Plus 1 upgrade.
- Acorn seemingly intended to release software in cartridge form as they had done for the Plus 1 (some of whose cartridges can run on the Master), but it appears that only Logo, OverView and ISO Pascal were released in this format. The slots are more usually used to hold cartridges such as those made by Acorn and Care Electronics which could carry standard 28 pin ROMs.
- ROMs connected via the cartridge slots are recognised as numbers 0 to 3 in the Master's ROM map.
Disc Interface
Shugart standard
MFM, double data density
FM, single data density
Supports 40 or 80 track drives with a 6ms step rate or better
Formatted capacity 320KB - MFM, 80 track, per surface total 1.28M on twin 80 track double-sided drives
34 way IDC connector
Network Interface
Acorn Econet
16K ANFS ROM
5 pin DIN socket
Printer Interface
8-bit Centronics compatible
26 way IDC connector
Serial Interface
RS-423 75-19200 software selectable baud rate
Independent transmit/receive baud rate selection
5 pin 'domino' DIN socket
Display
8 standard screen modes and 8 shadow modes providing the same displays without affecting user memory.
Graphics commands extend colour range by colour mixing.
Modes
| Mode | Colours | Graphics | Text |
|---|---|---|---|
| MODE 0 | 2 | 640x256 | 80x32 |
| MODE 1 | 4 | 320x256 | 40x32 |
| MODE 2 | 8 solid colours and 8 flashing colours | 160x256 | 20x32 |
| MODE 3 | 2 | N/A | 80x25 |
| MODE 4 | 2 | 320x256 | 40x32 |
| MODE 5 | 4 | 160x256 | 20x32 |
| MODE 6 | 2 | N/A | 40x25 |
| MODE 7 | N/A | 40x24 Teletext |
Outputs
Phono socket
UHF channel 36 full colour
BNC connector
Composite video 1V peak to peak, monochrome or colour with modification.
6 pin 'domino' DIN socket
RGB TTL level/+5V/positive or negative sync
Sound
4 channels with full software control
5cm internal speaker
User Port
10-bit memory mapped bi-directional TTL compatible port
+5 volts available
20 way IDC connector
1MHz Bus
General purpose bus extender
Audio input and output
34 way IDC connector
Tube
External
Custom interface for the connection of second processors
40 way IDC connector
Internal
Custom interface for the connection of co-processors
2x 12 way internal connectors
Internal or external Tube priority selectable by software
- The Master 128 could still use the 'cheese wedge' external Second Processors originally released for the earlier BBC Micro models thanks to the retention of the external 40 way Tube interface. In addition internal connectors on the motherboard could support an internal processor board, termed a Co-Processor to distinguish it from the earlier external boxes.
Analogue Input
4 channel analogue to digital conversion
8 bit accuracy
1.8V reference voltage
Light pen strobe connection to CRTC
Accepts external reference voltage for higher precision
15 way D-type connector
Cassette Interface
CUTS standard with 300-1200 software selectable baud rate
Output 200mV peak to peak
Input 50mV to 5V
Motor control relay 1 amp at 24 volts DC
7 pin DIN connector
Real Time Clock
Battery back-up Lithium cell, minimum 1 year life
- The rechargeable lithium cell was later replaced with three standard alkaline AA batteries. This configuration is by far the more common one. See below for more details.
Information can be called from MOS, BASIC and other languages
Time/Day/Date/Year
Keyboard
64-key QWERTY keyboard with 2 key rollover and auto repeat (rate and delay software selectable)
10 function keys
19 key numeric pad
Screwdriver-operated BREAK key lock
- The Master's keyboard is largely similar to that of the Model B. The differences include the addition of a numeric keypad to the right, the changing of the arrow keys to a more logical layout, and the shifting of the red function keys to the left to accomodate a hidden switch to disable the BREAK key. This last feature was added purportedly due to inadvertent operation of the key in schools, to which many students fell victim at some point.
Auxiliary power socket
+12 volts
+5 volts
-5 volts
Power available is dependent on internal options fitted.
Issue differences and variations
Unlike the Model B, the Master changed surprisingly little during its lifetime. There are only two motherboard versions and very few differences between them, with the issue 2 remaining the staple for the Master's entire life.
Very early machines used a rechargeable battery that fitted in the recess next to the cartridge slots to power the battery-backed CMOS. Allegedly due to embarassing incidents of Masters erupting in flames due to reverse current charging, Acorn changed this to regular AA cells, some in a re-usable battery box, others in a disposable shrink-wrapped pack placed next to the keyboard.
The connector at PL12 on the west side of the motherboard, originally designed with an internal modem in mind, is either nonexistent, a row of pins or a socket. The Master AIV or Domesday Machine requires the socket version for attachment of the internal SCSI board.
Some Masters have the system ROM soldered to the motherboard rather than socketed. This is uncommon.
