Expansion Subsystem, Appendix A

ERS II and ERS/FT II
Appendix A - Software Support

Expansion Subsystem Software Support

The A3470 host Expansion Subsystem interface card has a software addressable hardware port. It is mapped into 8-bit processor I/O address space as described in Chapter 3 -- Installation and Operation of this manual. The port is readable and writeable. The purpose of this control port is to provide a mechanism to remotely determine or modify the operational status of an attached Expansion Subsystem. In addition, the Expansion Subsystem may be isolated from the host ISA bus with this port. Status of the Expansion Subsystem Isolation, Reset, and Logic Power may be read from the control port.

Figure A-1 Interface Board Control Port.

Bit 0 Definition: Read/Write

A Logic 1 written to this bit isolates the attached Expansion Subsystem from the host by tri-stating inputs from control, interrupt, and DMA request lines, and tri-stating output lines from Data (D0-15) and Address (A0-19) to the Expansion Subsystem. A Logic 0 reconnects the Expansion Subsystem to the host.

Bit 0 may be read as follows: Logic 1 = Isolated Logic 0 = Not Isolated

While the subsystem is isolated from the host it can be powered off and on without affecting the host system. Maintenance can be performed as follows:

1. Write a logic 1 to bit 0 of the interface board's control port.

2. Read bit 0 - verify it is a logic 1 indicating that the subsystem is isolated.

3. Power down the subsystem.

4. Perform subsystem maintenance.

5. Power on the subsystem.

6. Write a logic 0 to bit 0 of the interface board's control port.

7. Read bit 0 - verify it is a logic 0 indicating that the subsystem is no longer isolated from the host.

Bit 1 Definition: Read Only

Bit 1 is the output of the Reset circuit to the attached Expansion Subsystem ISA Bus RESET DRV pin.

A Logic 1 indicates that the Expansion Subsystem is being held in reset for one of the following reasons: * Power at the Expansion Subsystem is off * The interface cable is disconnected * The RESET DRV signal on the host bus is set

A Logic 0 indicates the Expansion Subsystem is not in reset. Bit 2 Definition: Read Only

Bit 2 represents +5V from the Expansion Subsystem. A Logic 1 indicates that the attached Expansion Subsystem is powered on. A Logic 0 indicates the subsystem is powered off, or the interface cable is disconnected.

The Expansion Subsystem is ready to communicate with the host bus when:


        Bit 0  =  0
        Bit 1  =  0
        Bit 2  =  1

Bits 3 through 7 are not used.

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