Editing Sinclair ZX Spectrum +2 (section)

== Architecture ==

{| class="wikitable styled-table" style="width:70%; text-align:left;"
|+'''Sinclair ZX Spectrum +2 main devices'''
! Device !! Function
|-
| Zilog Z80A @ 3.5469 MHz || CPU
|-
| ULA || Video, keyboard scan, tape I/O and the beeper. Late machines may use a soldered '''Amstrad 40056''' instead of the usual Ferranti part
|-
| AY-3-8912A || Three channels of sound in addition to the ULA beeper; also provides bit-banged serial I/O
|-
| TEA2000 || Colour encoder
|-
| Amstrad 40057 || Dual joystick port interface
|-
| 128 KB DRAM || Eight 16 KB banks, paged into the Z80's address space
|}

Sources: Spectrum for Everyone and Tynemouth Software.<ref name="sfe" /><ref name="tyne" />

'''RAM numbering.''' This catches people out: many diagnostic tools report faults using 48K Spectrum IC numbers. On the +2, the '''upper set IC17–IC24 corresponds to IC15–IC22''' on a 48K Spectrum, and the '''lower set IC25–IC32 corresponds to IC13–IC6''' — note the reverse order.<ref name="tyne" />

'''Sound balance.''' As with all the 128K range, the mixing of the AY's three channels against the ULA beeper is not well balanced, and ULA sounds are usually much louder.<ref name="tyne" />

'''RAM contention.''' On the 128 and the grey +2, banks 1, 3, 5 and 7 are contended and 0, 2, 4 and 6 are uncontended — the opposite of what the official 128 specification stated. Software written against the real behaviour of these machines can therefore misbehave on the later +2A/+3, whose architecture matches the original specification.<ref name="sfe" />