External interface control circuitry for microcomputer systems

Details External interface control circuitry for microcomputer systems External interface control circuitry for microcomputer systems

G - Physics

06

F

354/221, 354/236

G06F 13/42 (2006.01) G06F 1/00 (2006.01) G06F 12/06 (2006.01) G06F 13/40 (2006.01)

Patent

CA 1233909

EXTERNAL INTERFACE CONTROL CIRCUITRY FOR MICROCOMPUTER SYSTEMS Abstract External interface control circuitry is described that couples a microcomputer system (100) to an external device (800). The control circuitry includes a microcomputer (102), a power switch (108) for applying power to the external device (800) in response to a PSC* signal, bus control (104) for gating interface signals from the microcomputer (102) with a PD* signal for application to the external device (800) and a peripheral interface adapter (106) for producing the PC and PD* signals and coupling the PI* and READY*/IRQ* signals to the microcomputer (102). A power-up sequence is executed by the microcomputer (102) in response to grounding the PI* signal when the external device (800) is plugged into the microcomputer system (100). Next, the external device (800) produces a binary zero state of the READY*/IRQ* signal, and in response microcomputer (102) produces a binary one state of the PD* signal and thereafter the PC signal. The sequence is then completed when the external device (800) returns the READY*/IRQ* signal to the binary one state. The unique power-up process insures that the external device (800) is only powered when present and protects CMOS devices in the interface control circuitry from being inadvertently destroyed.

483276

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