BBC  -   Master
at the end of the 8-bit era


The BBC Master was released by Acorn Computers in early 1986. It was designed as the successor to the BBC Micro Model B. The Master featured several improvements on its predecessor. The systems had 128 KB RAM as standard, to make it easier to use the best graphics modes. It had two cartridge slots mounted above the numerical keypad. Rather than the MOS Technology 6502 microprocessor used by the Model B it ran on the slightly improved 65C102: the cost of this CPU compatibility with the Model B was that the address bus was still only 16 bits, meaning that only 64 KB could be direct addressed at any one time and the remaining memory had to be paged in as required. However the 65C102's extra instructions allowed a little more to be shoehorned into the OS and BBC BASIC ROMs, limited by the memory architecture to 16 KB each.


 2 MHz Rockwell R65C102 processor
 128 KB ROM, consisting of 16 KB MOS (Machine Operating System), 
       always accessible, and seven 16 KB ROMs,
       any one of which could be paged into memory at a time:
     16 KB BBC BASIC
     16 KB Disk Filing System
     16 KB Advanced Disk Filing System
     16 KB Acornsoft View (word processor)
     16 KB ViewSheet (spreadsheet)
     16 KB Acorn Screen Editor AKA Edit (text/BBC BASIC editor)
     16 KB MOS extras (such as the cassette filing system)
 128 KB RAM, comprising:
     32 KB main user program/data storage
     20 KB "shadow" video memory (paged over main user RAM)
     12 KB OS workspace (paged over main user RAM)
     64 KB workspace accessible to user machine code applications 
       (in four 16 KB "Sideways" blocks any one of which could be paged 
       into memory if BBC BASIC the other paged ROMs not required)
 Full-travel keyboard with a top row of ten red-orange function keys  
       f0 - f9 and AT-style numeric keypad
 Highly configurable graphics display based on the Motorola 6845. 
       unlike on the original BBC Micro, separate video RAM was used.
 Four independent sound channels (one noise and 3 melodic) 
       using the Texas Instruments SN76489 sound chip
Graphic resolutions
Mode               Resolution   Hardware Colours Video RAM
     Char cells    (X-Y)Pixels
0     80  32      640  256        2          20      Graphics
1     40  32      320  256        4          20      Graphics
2     20  32      160  256        8          20      Graphics
3     80  25      640  200        2          16      Text
4     40  32      320  256        2          10      Graphics
5     20  32      160  256        4          10      Graphics
6     40  25      320  200        2            8      Text
7     40  25      240  250        8            1      (Teletext) Text

Built-in hardware support
 pluggable ROMs, directly or via cartridge slots
 floppy disk drives (DFS and ADFS) WD1770 disk controller
 tape interface (with motor control), 
 Centronics parallel printer
 serial communication (using RS-423, a superset of RS-232)
 display output for TV, RGB or 1v p-p video monitor
 A 15 pin 'D shaped' port with four analogue inputs 
    (suitable for joysticks, four digital/contact ports (for buttons) 
    and a special Light pen input, and
 proprietary "Tube" interface for internal or external 2nd CPU 
 a 16 pin IDC style "user port" 
     consisting of 8 general purpose digital I/O pins
 generic expansion through the "1 MHz bus".
 Econet interface, by adding a module board and ANFS ROM.
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