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<!-- edge connector table ends --> | <!-- edge connector table ends --> | ||
The [[ZX Spectrum + | 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 | 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 | 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==== | ||
Unlike the +3, the +2A and +2B have no floppy disc controller. Amstrad's original intention was to produce an external floppy controller addon which would have connected to the expansion port on these computers. Since the [[The Amstrad | Unlike the +3, the +2A and +2B have no floppy disc controller. Amstrad's original intention was to produce an external floppy controller addon which would have connected to the expansion port on these computers. Since the [[The Amstrad gate array|gate array]] is the same on all three machines, all the decoding logic is already present to generate the disk read/write and motor control signals. These three signals are therefore connected through to the expansion port. | ||
These signals occupy the pins which were originally used for the component video signals on the [[ZX Spectrum 16k/48k Edge Connector|16k/48k]] expansion port. | These signals occupy the pins which were originally used for the component video signals on the [[ZX Spectrum 16k/48k Edge Connector|16k/48k]] expansion port. | ||