|&FB7F||FDC 765 Data Register (read/write)
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Note: Bit b10 of the address port is reset as the FDC is seen as an expansion, even if it is an internal chip. Bit b7 is reset to select the FDC. Bits b8 and b0 are used to select the specific mode of operation. All other bits should be set to 1 to avoid conflict. [https://www.cpc-power.com/cpcarchives/index.php?page=articles&num=48 Source]
Note2: The [[Vortex Disc Drives|Vortex disc interface]] uses other ports. See its dedicated wiki page.
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* Execution Phase: During this phase, the actual data is transferred (if any). Usually that are the data bytes for the read/written sector(s), except for the Format Track Command, in that case 4 bytes for each sector are transferred. During data transfers between the FDC and the processor, the FDC must be serviced every 26µs (for MFM mode with CPC timings) or the FDC terminates the FDC command.
* Result Phase: Returns up to 7 result bytes (depending on the command) that are containing status information. The Recalibrate and Seek Track commands do not return result bytes directly, instead the program must wait until the Main Status Register signalizes that the command has been completed, and then it must (!) send a Sense Interrupt State command to 'terminate' the Seek/Recalibrate command. During the result phase, all the result bytes must be read. The FDC will not accept a new command until all the result bytes are read.
Note: Bit b10 of The Recalibrate and Seek Track commands do not return result bytes directly. Instead, the address port is reset as program must wait until the FDC is seen as an expansion, even if it is an internal chip. Bit b7 is reset to select Main Status Register signalizes that the FDCcommand has been completed. Bits b8 and b0 are used And then it must (!) send a Sense Interrupt State command to select 'terminate' the specific mode of operation. All other bits should be set to 1 to avoid conflict. [https:Seek//www.cpc-power.com/cpcarchives/index.php?page=articles&num=48 Source] Note2: The [[Vortex Disc Drives|Vortex disc interface]] uses other ports. See its dedicated wiki pageRecalibrate command.
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== Chip Variants == === IC Models used in CPC ===
More than one manufacturer made 765 compatible ICs. These are the ones known to be used in the CPC by looking at pictures of CPC mainboards. All should operate almost identically.
All the floppy disk drive models used by Amstrad are referenced here: [https://www.cpcwiki.eu/index.php/Amstrad_FDD_part Amstrad FDD part]
<br> == Chip = Other Variants ===
NEC has developed various successors to the original uPD765, such as the uPD72065, uPD72067, and uPD72069.
The КР1810ВГ72А is a Soviet clone of the Intel i8272. It is used in the [[Aleste 520EX]] clone of the Amstrad CPC computer.
=== Competitors ===
The main competitor of the µPD765 FDC chip on the market was the WD179x FDC chip family. Its main differences are: