User's Manual

PMAC User Manual
26 Talking to PMAC
Hardware Configuration PMAC PC, -VME
PMAC PC and -VME have an RS-422 interface on a 26-pin IDC connector (J4). This port connects
directly to a standard DB-25 connector on a host computer with a straight-across 26-strand flat-cable
connector. For a DB-9 host connector, a standard 9-to-25-pin adapter should be used on the other end of
the cable.
PMAC Lite
PMAC Lite has an RS-232 interface on a 10-pin IDC connector (J4). This port can connect directly with
a standard DB-9 connector on a host computer with a straight 10-strand flat-cable connector. For a DB-
25 host connector, a standard 25-to-9-pin adapter should be used on the other end of the cable. For an
RS-422 interface, the Option 9L piggyback board can be added. This provides a DB-25 connector for the
RS-422 port. The RS-232 port is disabled.
PMAC STD
PMAC STD has both an RS-232 interface on a 5-pin SIP connector (bottom board J1) and an RS-422
interface on a 20-pin mini-IDC connector (bottom board J3). Only one of these interfaces should be
connected at any one time.
PMAC 1.5 STD
PMAC 1.5 STD has an RS-232 interface on a 5-pin SIP and a 10-pin IDC connector; the 10-pin connector
can connect directly with a standard DB-9 connector on a host computer with a straight-across 10-strand
flat cable. It also has an RS-422 interface on a 26-pin IDC connector, which can connect directly with a
standard DB-25 connector on a host computer with a straight-across 26-strand flat cable.
RS-422 vs. RS-232
The PMAC RS-422 serial interface is very similar to the RS-232 interface that most PCs have. RS-422
has differential 0 to +5V signals, whereas RS-232 has single-ended -10 to +10V signals. The PMAC RS-
422 receivers accept inputs from RS-232 well, with significant noise margin. Most PCs’ RS-232
receivers can read the PMAC RS-422 signals quite well, but noise margin tends to be minimal, and
communications in this direction can be garbled, especially in the presence of PWM amplifiers. For
robust communications to an RS-232 host, PMAC Acc-26 provides conversion capabilities and optical
isolation. Of course, direct connection to a host RS-422 port can be made.
Baud Rate
The serial-port baud rate is determined at power-up by jumpers E44-E47 (PMAC PC, Lite, 1.5 STD,
VME) or switches SW1-1 to SW1-4 (PMAC STD), and the PMAC master clock rate. Serial baud rate
can be set up to 76,800 baud on a 20 or 40 MHz board, up to 115,200 baud on a 30 or 60 MHz board. If
E44- E47 are all ON (SW1-1 to SW1-4 all OFF), the serial port is disabled.
Signal Lines
Since serial interfaces vary from system to system, PMAC provides a simple but flexible interface. In
addition to the signal ground, only four lines are required (eight counting the complements): data-
transmit, data-receive, clear-to- send, and ready-to-send. These pairs of lines may be exchanged through
jumpers (E9-E16), if necessary, to match the host configuration. PMAC simply shorts together the DSR
and DTR lines to provide an automatic return signal on this strobe for those systems that require it.
Data Format
The serial communications data format is eight bits, one start bit, one stop bit, with no parity if jumper
E49 is ON, or odd parity if jumper E49 is OFF (opposite for PMAC STD). PMAC can echo back to the
host each character it receives from the host; the <CTRL-T command toggles this function on and off.
No XON/XOFF handshaking is supported. Line-by-line checksums can be computed. Variable I4
controls this function.