used to select the IRQ for serial port 1 (bits 7:4)
and for serial port 2 (bits 3:0). Refer to IRQ
Table for CR27. Any unselected IRQ output
(registers CR27 - CR29) is in tristate.
CR27
This register can only be accessed in the
Configuration Mode and after the CSR has been
initialized to 27H. The default value of this
register after power up is 00H. This register is
used to select the IRQ for the FDC (Bits 4:7)
and the parallel port (bits 3:0). Any unselected
IRQ output (registers CR27-CR29) is in tristate.
To properly share an IRQ among UART1 and
UART2:
1)
Configure UART1 to use the desired
IRQ pin.
2)
Set UART2 to 0Fh i.e., set CR28
bits[3:0]=1111. This selects the share
IRQ mechanism. Refer to Table 60 on
the following page:
CR28
This register can only be accessed in the
Configuration Mode and after the CSR has been
initialized to 28H. The default value of this
register after power up is 00H. This register is
D3-D0 or
D7-D4
IRQ Selected
None
0000
0001
0010
0011
0100
0101
0110
0111
1000
IRQ_A
IRQ_B
IRQ_C
IRQ_D
IRQ_E
IRQ_F
Reserved
IRQ_H
used to select the IRQ for IRQIN (bits 3:0).
Refer to IRQ Table for CR27. Bits 7:4 are
CR29
This register can only be accessed in the
Configuration Mode and after the CSR has been
initialized to 29H. The default value of this
register after power up is 00H. This register is
reserved and return zero when read.
Any
unselected IRQ output (registers CR27-CR29) is
in tristate.
135
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