multiplexing serial communications
ast0 at isa? port 0x1a0 irq 5
ast1 at isa? port 0x2a0 irq 6
com* at ast?
driver provides support for boards that
multiplex together up to four EIA RS-232C (CCITT V.28) communications
interfaces. Apparently the original master of hardware using this multiplexing
protocol was AST.
device is the master device for up to four
devices. The kernel configuration specifies
devices as slave devices of the
device, as shown in
. The slave ID given for
device determines which bit in the
interrupt multiplexing register is tested to find interrupts for that device.
The port specification for the ast
device is used
to compute the base addresses for the com
subdevices and the port for the interrupt multiplexing register.
On a real AST card, the jumpers are as follows:
- Turn ON for irq 2. Default is OFF.
- Turn ON for irq 3. Default is OFF.
- Turn ON for irq 4. Default is OFF.
- Turn ON for irq 5. This is ON for the first card, OFF
- Turn ON for irq 6. This is ON for the second card, OFF
- Turn ON for irq 7. Default is OFF.
- “Compatible mode”. The
ast driver needs extended mode, so leave this
- I/O Address. In extended mode, this should be OFF for the
first card at 0x1a0-0x1a7 and ON for the second card at 0x2a0-0x2a7.
- Interrupt sharing. Default is OFF.
- Reserved, must be OFF.
driver was written by Roland McGrath and
placed into the public domain.