cxb(4)
NAME
cxb − CXB16 communications interface
SYNTAX
device dhu0 at uba0 csr 0160440 flags 0xffff vector dhurint dhuxint
DESCRIPTION
A CXB16 provides 16 data leads-only communication lines with no modem control. The CXB16 conforms to RS422A. The device behaves and looks just like a DHV11 (with the exception of modem control and number of lines) and is specified in the configuration line the same as a DHV11 device. Each line attached to the CXB16 communications interface behaves as described in tty() and may be set to run at any of 16 speeds. See tty() for the encoding.
A flags field of 0xffff must be used to specify that all lines are to operate as hardwired. This is done to prevent the line from being treated as a modem control line.
The dhu driver normally interrupts on each input character.
NOTE
The cxa, cxb, cxy, dhv, and dhq devices operate under the control of the dhu driver.
DIAGNOSTICS
dhu%d: receive fifo overflow. The character input fifo 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. This may cause a few input characters to be lost to users. It is not serious.
dhu%d:%d DMA ERROR. A DMA transfer error has occurred. The cxb unit number and line number are printed. This means that the channel indicated has failed to transfer DMA data within 10.7 microseconds of the bus request being acknowledged, or that there is a memory parity error. This may cause a few output characters to be lost.
dhu%d: DIAG. FAILURE. This indicates that the cxb internal diagnostics have detected an error. The cxb failed to clear the start bit. Normally this is cleared to signal that a DMA transfer has completed.
FILES
/dev/tty??