DH(4) DH(4) NAME dh - DH-11/DM-11 communications multiplexer SYNOPSIS device dh0 at uba0 csr 0160020 vector dhrint dhxint device dm0 at uba0 csr 0170500 vector dmintr DESCRIPTION A dh-11 provides 16 communication lines; dm-11’s may be optionally paired with dh-11’s to provide modem control for the lines. Each line attached to the DH-11 communications multiplexer behaves as described in _t_t_y(4). Input and output for each line may independently be set to run at any of 16 speeds; see _t_t_y(4) for the encoding. Bit _i of flags may be specified for a dh to say that a line is not properly connected, and that the line should be treated as hard-wired with carrier always present. Thus specifying ‘‘flags 0x0004’’ in the specification of dh0 would cause line ttyh2 to be treated in this way. The _d_h driver monitors the rate of input on each board, and switches between the use of character-at-a-time interrupts and input silos. While the silo is enabled during periods of high-speed input, the driver polls for input 30 times per second. FILES /dev/tty[h-o][0-9a-f] /dev/ttyd[0-9a-f] SEE ALSO tty(4) DIAGNOSTICS dh%d: NXM. No response from UNIBUS on a dma transfer within a timeout period. This is often followed by a UNIBUS adapter error. This occurs most frequently when the UNIBUS is heavily loaded and when devices which hog the bus (such as rk07’s) are present. It is not serious. dh%d: silo overflow. The 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 mes‐ sage on the console with interrupts disabled. It is not serious. 4th Berkeley Distribution May 16, 1986 DH(4)