Technical data

zsh(7D) Devices SunOS 5.5
NAME zsh − On-board serial HDLC/SDLC interface
SYNOPSIS #include <fcntl.h>
open(/dev/zshn, mode );
open(/dev/zsh, mode );
AVAILABILITY SPARC
DESCRIPTION The zsh module is a loadable STREAMS driver that implements the sending and receiving
of data packets as HDLC frames over synchronous serial lines. The module is not a stan-
dalone driver, but instead depends upon the zs module for the hardware support
required by all on-board serial devices. When loaded this module acts as an extensionto
the zs driver, providing access to an HDLC interface through character-special devices.
The zshn devices provide what is known as a data path which supports the transfer of
data via read(2) and write(2) system calls, as well as ioctl(2) calls. Data path opens are
exclusive in order to protect against injection or diversion of data by another process.
The zsh device provides a separate control path for use by programs that need to
configure or monitor a connection independentof any exclusive access restrictions
imposed by data path opens. Up to three control paths may be active on a particular
serial channel at any one time. Control path accesses are restricted to ioctl(2) calls only;
no data transfer is possible.
When used in synchronous modes, the Z8530 SCC supports several options for clock
sourcing and data encoding. Both the transmit and receive clock sources can be set to be
the external Transmit Clock (TRxC), external Receive Clock (RTxC), the internal Baud
Rate Generator (BRG), or the output of the SCC’s Digital Phase-Lock Loop (DPLL).
The Baud Rate Generator is a programmable divisor that derives a clock frequency from
the PCLK input signalto the SCC. A programmed baud rate is translated into a 16-bit
time constant that is stored in the SCC. When using the BRG as a clock source the driver
may answer a query of its current speed with a value different from the one specified.
This is because baud rates translate into time constants in discrete steps, and reverse
translation shows the change. If an exact baud rate is required that cannot be obtained
with the BRG, an externalclock source must be selected.
Use of the DPLL option requires the selection of NRZI data encoding and the setting of a
non-zero value for the baud rate, because the DPLL uses the BRG as its reference clock
source.
A local loopback mode is available, primarily for use by the syncloop(1M) utility for
testing purposes, and should not be confused with SDLC loop mode, which is not sup-
ported on this interface. Also, an auto-echo feature may be selected that causes all
incoming data to be routed to the transmit data line,allowing the port to act as the
remote end of a digital loop. Neither of these options should be selected casually, or left
in use when not needed.
7D-416 modified 20 Jan 1993