US 4,794,525 A · 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.

Claims39

Dependent claims

Interface control circuitry for coupling processing means interface signals to an external device that is insertable in said interface control circuitry, said external device having means for producing an indication signal when the external device is inserted and coupled to the processing means interface signals, and said external device having means for producing a ready signal in response to the application of power to the external device, said interface control circuitry comprising:

switching means for applying power to the external device in response to a power control signal;
gating means for applying the processing means interface signals only in response to an interface control signal;
and
processing means for producing the processing means interface signals, said processing means being rssponsive to the external device indication signal for producing the power control signal and a predetermined time delay, and after the predetermined time delay has elapsed, said processing means being responsive to the external device ready signal for producing the interface control signal.

1 more element

A system comprising in combination:

(a) an external device that is insertable in said system comprising:
(i) means for producing an indication signal indicating that the external device is inserted in said system and coupled to processing means interface signals;
and
(ii) means for producing a ready signal in response to the application of power to the external device;
(b) processing means for producing the processing means interface signals, said processing means being responsive to the external device indication signal for producing a power control signal and a predetermined time delay, and after the predetermined time delay has elapsed, said processing means being responsive to the external device ready signal for producing an interface control signal;
and
(c) interface control circuitry coupled to said processing means and said external device, comprising:
(i) switching means for applying power to the external device only in response to the power control signal;
and
(ii) gating means for applying the processing means interface signals only in response to the interface control signal.

7 more elements

Dependencies are inferred from the claim text.

External interface control circuitry for microcomputer systems

Life of this patent

External interface control circuitry for microcomputer systems

Life of this patent

Abstract

Claims39