Editing Acorn Electron (section)

== Architecture ==

The Electron centred on a custom Ferranti ULA (Uncommitted Logic Array) of about '''2,400 gates''', handling video generation, RAM control, sound, cassette I/O, keyboard scanning, clock division and reset.<ref name="wp" /> Integration came at a performance cost: the memory is 4&nbsp;bits wide (four 64K×1 DRAMs), so each byte needs two accesses, and the CPU can access RAM only at 1&nbsp;MHz &mdash; and is halted entirely while the ULA reads RAM during the active display.<ref name="wp" /><ref name="sm">[[Acorn Electron Service Manual]] (Part no. 0405001, Issue 2, January 1987), Acorn Computers &mdash; hosted on this wiki. Source for the IC complement (IC1 ULA 12C021 in a 68-pin holder, IC2 single 32&nbsp;KB OS/BASIC ROM, IC3 6502A, IC4&ndash;7 4164 DRAM, IC8 74S04 16&nbsp;MHz oscillator, IC13 LM324), the 16&nbsp;MHz clocking, the 19&nbsp;V&nbsp;AC 14&nbsp;W supply and +5&nbsp;V/&minus;5&nbsp;V rails, the capacitor list, and that the machine will not run without the keyboard connected.</ref>

=== Memory map ===

{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+'''Acorn Electron memory map'''
! Address Range !! Size !! Function
|-
| $0000 – $00FF || 256 bytes || Zero page
|-
| $0100 – $01FF || 256 bytes || 6502 stack
|-
| $0200 – $03FF || 512 bytes || OS and VDU workspace
|-
| $0400 – $07FF || 1 KB || Current-language (BASIC) workspace
|-
| $0800 – $0DFF || 1.5 KB || Buffers and NMI workspace
|-
| $0E00 – $7FFF || up to ~29 KB || User program and screen memory (mode-dependent)
|-
| $8000 – $BFFF || 16 KB || Paged (sideways) ROM/RAM &mdash; BBC BASIC II
|-
| $C000 – $FFFF || 16 KB || Operating system ROM (MOS 1.0)
|}