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ZX Spectrum 128

7 bytes added, 00:03, 10 November 2015
Proper name of Spectrum 128
{{See Also|the "toastrack" 128K modeloriginal Spectrum 128|other Spectrum models with 128K 128kB of RAM|ZX Spectrum 128K models}}
{{Infobox computer
| cpu = [[Z80|Z80A]] @ 3.5469MHz
*Processor: Zilog Z80A microprocessor clocked at 3.5469MHz.
*ROM: 32KB 32kB ROM, arranged in 2 pages of 16KB16kB.*RAM: 128KB 128kB of Dynamic RAM, arranged in 8 pages of 16KB16kB.
*Graphics: 256 × 192 pixels, 16 colours, attribute based. See [[Spectrum Video Modes]].
*Sound: [[AY-3-8912]] 3 channel, 8 octave Programmable Sound Generator and "beeper". Modulated onto video signal.
The memory space of the ZX Spectrum+ 128K 128 is divided into four 16k 16kB pages. The 32k 32kB of ROM and 128k 128kB of RAM can be paged into the memory space as shown in the diagram below:
<!-- table of memory pages -->
== HAL bugs ==
Reads from port 0x7ffd cause a crash, as the 128K128's HAL10H8 chip does not distinguish between reads and writes to this port, resulting in a floating data bus being used to set the paging registers.
Due to a bug either in the 128K128's HAL10H8 chip or in the 128K PCB, memory banks 1, 3, 5 and 7 are contended (and the rest uncontended) as opposed to 4, 5, 6 and 7 as documented in the service manual. Whereas the +2 (with grey case) shares this behaviour, the +2A and +3 apply contention to pages 4–7 instead. The paging scheme documented in the manual would have been implemented as was (presumably) originally intended had the B0 and B2 inputs to the HAL10H8 been reversed, either on the 128K Spectrum 128 PCB or in the logic of the HAL itself.
Later grey +2s were shipped with an updated HAL chip which corrects there issue whereby reads of port 0x7ffd would crash the machine[]. It is not known whether this also updated the contention scheme to contend on pages 4–7.
The 128K Spectrum 128 suffers from a "rain" effect when the Z80's I register is set to a memory address within the region of 0x4000–0x7fff. Velesoft's "Umbrella" GAL[] corrects this rain effect as well as the crash that results when reading from port 0x7ffd, although it does not change the set of pages that are contended. For the rain effect to be corrected, a flying lead must be connected between the Z80's {{overline|RFSH}} signal and the GAL.
== Keypad ==
The keypad released for Investronica's Spanish 128K 128 has been found to be incompatible with at least some UK 128K machines. Issue 6K boards provide the wrong voltage to the keypad. This is fixed in Issue 6U by replacing R137.

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