AST(4) | Device Drivers Manual | AST(4)

# NAME

`ast` — multiplexing serial communications interface

# SYNOPSIS

`ast0 at isa? port 0x1a0 irq 5`
`ast1 at isa? port 0x2a0 irq 6`
`com* at ast?`

# DESCRIPTION

The `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.

Each `ast` device is the master device for up to four `com` devices. The kernel configuration specifies these `com` devices as slave devices of the `ast` device, as shown in SYNOPSIS. The slave ID given for each `com` 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:

SW1-1
  Turn ON for irq 2. Default is OFF.
SW1-2
  Turn ON for irq 3. Default is OFF.
SW1-3
  Turn ON for irq 4. Default is OFF.
SW2-1
  Turn ON for irq 5. This is ON for the first card, OFF otherwise.
SW2-2
  Turn ON for irq 6. This is ON for the second card, OFF otherwise.
SW2-3
  Turn ON for irq 7. Default is OFF.
SW3-1
  “Compatible mode”. The `ast` driver needs extended mode, so leave this OFF.
SW3-2
  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.
SW3-3
  Interrupt sharing. Default is OFF.
SW3-4
  Reserved, must be OFF.

# FILES

/dev/tty0?

# SEE ALSO

com(4), intro(4), isa(4)

# HISTORY

The `ast` driver was written by Roland McGrath and placed into the public domain.

May 21, 2008 | Debian