fc(4) — VAX
Name
fc − VAXstation serial line interface
Syntax
device fc0 at ibus? flags 0x0f vector fcxrint
Description
This serial line interface is similar to the DZQ11 four-line communications multiplexer. An fc interface provides four communication ports with partial modem control on port 2, adequate for dialup use. Only port 2 supports modem control (dialup access), all other ports must be operated as local lines. Each line attached to the serial line controller behaves as described in tty() and may be set to run at any of 16 speeds. For the encoding, see tty(.). However, configuration requirements dictate fixed speed operation of ports connected to the console terminal and graphics devices.
The fc ports are configured as follows:
Port Usage
0 Graphics device keyboard at 9600 BPS
1 Mouse or tablet at 4800 BPS
2 Communications (with modem control)/local terminal
3 Serial printer port at 9600 BPS
A diagnostic console terminal may be connected to port 3. When the diagnostic console is in use, the processor may be halted by pressing the BREAK key. The selection of which port to use for the console is made during the processor’s power on sequence and cannot be changed after power on. If the Low End Graphics Subsystem (LEGSS) console is present, it will be used; otherwise the device connected to port 3 will be the console.
For the fc device, the flags should always be specified as “flags 0x0f” (all 4 lines hardwired). The state of port 2 may be established by specifying either modem or nomodem as part of the /etc/ttys file entry for tty02; see ttys(.). The default state of port 2 may be controlled by flags bit 2. Set “flags 0x0f” for a hardwired line, “flags 0x0b” for dialup operation (wait for carrier).
The fc driver operates in interrupt-per-character mode (all pending characters are flushed from the silo on each interrupt). Silo alarm mode is used by the DZQ11 driver at times of high input character traffic. This mode is not used by the fc driver, due to the need to track mouse or tablet position changes in real time.
Restrictions
Speed must be set to 9600 BPS on the console port, 9600 BPS on the keyboard port, and 4800 BPS on the mouse port. The fc driver enforces this restriction; that is, changing speeds with the stty command may not always work on these ports.
Diagnostics
fc0: input silo overflow
The 64-character input silo overflowed before it could be serviced. This can happen if a hard error occurs when the CPU is running with elevated priority, as the system will then print a message on the console with interrupts disabled.
Files
/dev/consoleconsole terminal or graphics device
/dev/tty00not used
/dev/tty01local terminal - multiuser configuration only
/dev/tty02dialup or local terminal
/dev/tty03printer port or local terminal
/dev/mousemouse or tablet - workstation configuration only
/dev/fcscreenconsole message window for workstations