dc(4) - NetBSD Manual Pages

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DC(4)                NetBSD/pmax Kernel Interfaces Manual                DC(4)


NAME

     dc - dc659, dc7085 DZ11-on-a-chip serial communications interface


SYNOPSIS

     dc* at ibus0 addr ?


DESCRIPTION

     The dc driver provides support for Digital's dc7085 four-port serial com-
     munications chip.  The dc driver supports dc7085 hardware found on the
     DECstation 2100, 3100, 5100, the optional expansion devices on the 5100,
     and the DECstation 5000/200.

     The dc device is in essence a single-chip clone of the DZ-11.  The DZ-11
     hardware design severely constrains performance because it has one small
     input silo that is shared across all ports.  The dc hardware does not
     interrupt on modem transitions; instead, they must be detected by polling
     the device.  Only two ports on a baseboard dc device have any modem con-
     trol signals; the other two ports are wired for a keyboard and mouse.


SEE ALSO

     ibus(4), intro(4)


HISTORY

     The dc driver first appeared in 4.4BSD.  This manual page first appeared
     in NetBSD 1.2.


BUGS

     On some implementations (e.g. DECstation 3100), the hardware does not
     bring out modem flow-control signals (RTS/CTS) to the bulkhead; only
     modem carrier transition are provided.  This is adequate for UNIX dial-in
     and dial-out detection, but without hardware flow control, the dc device
     is prone to input silo overruns when used for serial-line protocols at
     high speed.  The DECstation 5000/200 dc hardware provides full modem con-
     trol on both bulkhead RS-232 ports and is thus less prone to input silo
     overrun.

     The 19200 speed on all dc devices is actually implemented as 19800, pre-
     sumably for bug-compatibility with the original DZ-11.  This is a hard-
     ware "feature" and cannot be corrected in software.  Many serial devices
     at 19200 fail to interoperate with the dc at its 19800 speed setting.

     The DECstation 5000/200 can set a bit in the system register to allow the
     dc to run at 38400, but this applies to all four ports and disables the
     19200 speed on all four ports.  This feature is not currently supported.

     The dc driver should be merged into a single driver supporting the origi-
     nal DZ-11, DZ-32, and Qbus DZV-11 and DZQ-11 clones.

NetBSD 2.0                     February 20, 1998                    NetBSD 2.0