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System Specification for C65Fred BowenMarch 1, 1991

2.3.5.6 FAST SERIAL MODE

The EAST SERIAL logic consists of a 2-bit write-only register, which resides in location 0001 (hex). This register may only, be accessed by the CPU if neither the AEC or DMA/ line is low. Upon reset, both bits in the register are forced low which allows the device to operate as normal (the CNTA, SPA, PRC57 and FLAGA/ lines will not be affected).

Bit 7 of the FAST SERIAL register is the Fast Serial Mode disable bit (DMODE* bit).

Bit 6 of the FAST SERIAL register is the FSDIR* bit. When the DMODE* bit is set high, the FSDIR* bit will be used as an output to control the fast serial data direction buffer hardware, and as an input to sense a fast disk enable signal. This function will affect the CNTA, SPA, PRC57 and FLAGA/ lines as summarized in the following table.

DMODE*FSDIR*FUNCTION
0 0 Fast Serial mode is disabled.
x 1 Both the FLAGA/ and the PRC57 lines will behave as outputs. The FLAGA/ output will reflect the state of the CNTA pin, whereas the PRC57 output will reflect the state of the SPA pin.
1 0 Both the CNTA and SPA lines will behave as outputs. The CNTA ouput will reflect the state of the FLAGA/ pin, whereas the SPA output will reflect that of the PRC57 pin.



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