Octagon PC-510, User Manual

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5-4
Serial ports PC-510 user’s manual
2. Determine the interrupt status port address based on bit 5 (I/O range
select A) and bit 4 (I/O range select B) at register 0A9h. See the table
below.
Table 5-6 Reading the interrupt status port: Register 0A9h
I/O range
select
A† B†
COM3
addresses COM4
addresses COM5
addresses COM6
addresses
Interrupt
status
port
*( *( '() () ()
'' *( *( '( ( (
' *( *( '( ( (
' *( *( '( ( (
)/
j/Z [\/q@Z []/q
For example, if bits 5 and 4 are both 1, the interrupt status port address
is 338h (default). If bits 5 and 4 are both 0, the interrupt status port
address is 158h; if bit 5 is 0 and bit 4 is 1, the address for the interrupt
status port is 138h; and if bit 5 is 1 and bit 4 is 0, the address for the
interrupt status port is at 358h.
3. Inside your interrupt handler, read the interrupt status port. Bit 0
through bit 3 show which serial port caused the interrupt.
For example, when there is a 1 in bit 3, this means COM3 caused the
interrupt; a 1 in bit 2 shows that the interrupt came from COM4; a 1 in
bit 1 means that COM5 caused the interrupt; and by default, when a 1 is
in bit 0, then COM6 caused the interrupt. See the table above to read
the interrupt status port.
Note Exit the interrupt handler only when bits 0 through 3 are all at 0.
Table 5-7 Interrupt status port (138h, 158h, 338h, and 358h)
Bit Location
' #
Note All 0s as bits indicate no interrupt and a 1 indicates an interrupt.
It is possible to change the interrupt through the IRQ routing matrix.
You can also change bits 4 and 5 I/O ranges, COM5 and COM6
addresses, and the status port addresses through the IRQ routing matrix.
See the
IRQ routing and opto IRQs chapter for more details on how to
change and reroute base addresses.