ZX Spectrum +2A/2B, +3/3B edge connector: Difference between revisions

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The [[ZX Spectrum +3/2A/2B|ZX Spectrum +2A/+3 and +2B]] [[:category:Edge Connectors|expansion connector]] is a double sided card edge connector with a 0.1 inch spacing. The two rows of conductors are numbered from right to left looking into the rear of the computer.
The [[ZX Spectrum +2A/2B, +3/3B|ZX Spectrum +2A/+3, +2B, and +3B]] [[:category:Edge Connectors|expansion connector]] is a double sided card edge connector with a 0.1 inch spacing. The two rows of conductors are numbered from right to left looking into the rear of the computer.
One pair of conductors are missing as there is an [[#Key Slot|indexing slot]] cut out of the circuit board.
One pair of conductors are missing as there is an [[#Key Slot|indexing slot]] cut out of the circuit board.


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====CPU Clock====
====CPU Clock====
The CKEXT signal is available on Lower Pin 8. The CPU clock signal is generated by the [[The Amstrad gate array|gate array]] (IC1) and is interrupted during [[contended memory]] access. This clock signal is fed into the Z80 via a series resistor. The CKEXT signal is inverted in relation to the CPU clock as it has been passed through a NOT gate.
The CKEXT signal is available on Lower Pin 8. The CPU clock signal is generated by the [[The Amstrad gate array|gate array]] (IC1) and is interrupted during [[contended memory]] access. The CKEXT signal is inverted in relation to the CPU clock input.


====Key Slot====
====Key Slot====
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====ROM disable pins====
====ROM disable pins====
All the previous models of ZX Spectrum have a single ROM chip which could be disabled to facilitate paging in external memory by pulling the {{overline|ROMCS}} line high. The +2A/+3 and +3B however have two ROM chips and brings them out to independent pins on the expansion port. The old {{overline|ROMCS}} pin (Lower pin 25) is not used, and instead Upper pin 4 and Lower pin 15 are used. These pins were both unused on the [[ZX Spectrum 128K Edge Connector|128k+]], however Lower pin 15 was used for composite video out on the [[ZX Spectrum 16k/48k Edge Connector|16k/48k]].
All the previous models of ZX Spectrum have a single ROM chip which could be disabled to facilitate paging in external memory by pulling the {{overline|ROMCS}} line high. The +2A/+3 and +3B however have two ROM chips and brings them out to independent pins on the expansion port. The old {{overline|ROMCS}} pin (Lower pin 25) is not used, and instead Upper pin 4 and Lower pin 15 are used. These pins were both unused on the [[ZX Spectrum+ 128K edge connector|128K]], however Lower pin 15 was used for composite video out on the [[ZX Spectrum 16K/48K edge connector|16K/48K]].


====Disc Controller Signals====
====Disc Controller Signals====

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