Editing Sinclair ZX Spectrum 128 (section)

== Architecture ==

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''ZX Spectrum 128 main devices (Service Manual Table 5.4)'''
! Ref !! Device !! Function
|-
| IC1 || Ferranti '''7C001''' ULA || Video, keyboard scan, tape I/O, beeper
|-
| IC2 || '''Z80A''' / µ780 (Zilog or NEC) || CPU at 3.5469 MHz
|-
| IC5 || '''SPECTRUM 128''' ROM (VTI) || 32 KB; pin-compatible with a 27256 EPROM, address access &lt;400 ns, output-enable access &lt;250 ns
|-
| IC6–IC13 || '''4164''' DRAM, 150 ns || Contended RAM bank
|-
| IC15–IC22 || '''4164''' DRAM, 150 ns || Uncontended RAM bank
|-
| IC27 || '''ZX8401''' (Mullard) || Address multiplexing / glue logic
|-
| IC29 || '''HAL10H8CN''' || Address decode
|-
| IC30 || 74LS157 (not National) || RAM multiplexer
|-
| IC32 || '''AY-3-8912A''' (General Instrument) || Three-channel sound
|-
| IC33 / IC34 || '''MC1488''' / '''MC1489''' || RS-232 and keypad line driver / receiver
|-
| IC36 || '''TEA2000''' (Philips) || Colour encoder
|-
| IC38 || '''MC1376''' (Motorola) || UHF modulator driver
|-
| X1 || '''17.734475 MHz''' crystal || Master clock; series resonant with 20 pF, ±10 ppm absolute
|}

All RAM must be '''150 ns access time with 128-row refresh'''. The Service Manual lists Hitachi, Intel, Mitsubishi, Mostek, Motorola, NEC, OKI, Panasonic, Toshiba and National as acceptable manufacturers.<ref name="sm128">''ZX Spectrum 128 Service Manual'', Sinclair Research Ltd. Hosted on this wiki as [[Sinclair ZX Spectrum 128 Service Manual]] ([[:File:ZX Spectrum 128 Service Manual.pdf|PDF]]). Source for the parts lists (Table 5.3 case assembly, Table 5.4 main PCB, Table 5.5 keypad PCB) and the notes to Table 5.4; the RAM specification; section 1.10, the on-board power supply description; the clock frequencies; the section 4.2 basic-checks and fault-finding procedure; and the section 4.3 repair notes.</ref>

The numeric keypad is not a passive matrix — it has its own PCB carrying a '''General Instrument PIC1652''' microcontroller, a 68 µH Toko coil and its own zener-regulated supply.<ref name="sm128" />

=== Memory contention ===

Despite what the official 128 specification says, on real Toastrack hardware '''banks 1, 3, 5 and 7 are contended and banks 0, 2, 4 and 6 are uncontended'''. Software written and tested on real 128s therefore behaves differently on the later +2A/+3, whose architecture matches the published specification — most audibly as distorted beeper audio or sampled speech.<ref name="sfe" />