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Card Selected Feedback
When the adapter is addressed, it responds by setting the '-card
selected feedback' signal
(-CD SFDBK)
to active.
-CD SFDBK
is derived
from the address decode and driven by a totem pole driver. It is
latched by the system board and can be read through the Card
Selected Feedback register at address hex 0091. Diagnostic and
automatic configuration programs use this signal to verify the
operation of an adapter at a given address or DMA port. This signal
must not be active during a setup cycle.
The Card Selected Feedback register is a read-only register at
address hex 0091. It allows programs to monitor
-CD SFDBK
and
thereby determine if the video subsystem, system board 110, or an
adapter is addressed and functioning.
Bit
Function
7 - 1
Reserved
o
-Card Selected Feedback
Figure
2-2. Card Selected Feedback Register (Hex 0091)
Bits 7 • 1
Reserved.
Bit 0
This bit is set to 1 whenever
-CD SFDBK
was active on a
previous cycle or whenever the system board I/O
functions (diskette drive, serial, or parallel interfaces) are
accessed by an I/O cycle. Reading this register resets the
bit to O.
System Board Setup
The integrated I/O functions on the system board use POS
information during setup. The diskette drive controller, serial port,
and parallel port are treated as a single device. The video subsystem
is also an integrated part of the system board; however, POS treats it
as a separate device. The System Board EnablelSetup register is
used to place the system board or video subsystem into the setup
mode.
2·6
Model 50 POS
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