Note A. Logical Device IRQ and DMA Operation
1.
IRQ and DMA Enable and Disable: Any time the IRQ or DACK for a logical block is
disabled by a register bit in that logical block, the IRQ and/or DACK must be disabled. This
is in addition to the IRQ and DACK disabled by the Configuration Registers (active bit or
address not valid).
a.
FDC: For the following cases, the IRQ and DACK used by the FDC are disabled (high
impedance). Will not respond to the DREQ
Digital Output Register (Base+2) bit D3 (DMAEN) set to "0".
The FDC is in power down (disabled).
b.
c.
Serial Port 1 and 2:
Modem Control Register (MCR) Bit D2 (OUT2) - When OUT2 is a logic "0", the serial port
interrupt is forced to a high impedance state - disabled.
Parallel Port:
I.
SPP and EPP modes: Control Port (Base+2) bit D4 (IRQE) set to "0", IRQ is
disabled (high impedance).
ECP Mode:
ii.
(1)
(2)
(DMA) dmaEn from ecr register. See table.
IRQ - See table.
MODE
(FROM ECR REGISTER)
IRQ PIN
PDREQ PIN
CONTROLLED BY CONTROLLED BY
000
001
010
011
100
101
110
111
PRINTER
IRQE
IRQE
(on)
dmaEn
dmaEn
dmaEn
dmaEn
dmaEn
dmaEn
dmaEn
dmaEn
SPP
FIFO
ECP
(on)
EPP
IRQE
IRQE
(on)
RES
TEST
CONFIG
IRQE
d.
Keyboard Controller: Refer to the KBD section of this spec.
146
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