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PSI System Controls and Diagnostics
21 Communications Protocols
21.1 Overview
The F100 supports three types of communication protocol, selected according to the setting of
the mode switch:
a) An eight bit ASCII protocol, messages compliant with SCPI. The low seven bits are used to
encode the ASCII character. The eighth bit is only set for synchronization when the <ACK>,
<BELL>, <CR>, <LF>, and <ESC> characters are transmitted.
b) An eight bit binary protocol. The first and last bytes of the entire command or reply have the
eighth bit set and contain the address. All other bytes in the messages are broken into two bytes,
encoded into the low nibble (4 bits), thus never having the top bit set.
c) A nine bit binary protocol. Synchronization is done with the ninth bit. The first and last byte
of each message have the ninth bit set and contain the address, and all other bytes are unmodified
binary (with the ninth bit clear).
ASCII messaging is provided for users who wish to use existing host software systems that
provide convenient support for ASCII communications. All the capabilities of the F100 are
available through a familiar virtual instrument model and message structure. A simple terminal
program such as Windows Hyperterminal is sufficient to establish communication with the
device. It is possible to communicate with multiple devices at different addresses on the same
channel by selecting a particular address to be the listener device at any time.
The binary messaging is more efficient in its use of communications bandwidth. It is fully
deterministic with embedded addressing in the messages and immediate responses, including
error reports, from the devices. Pyramid provides software drivers and diagnostic host programs
for users who wish to use binary communication protocols. Eight bit binary is primarily intended
for direct host to device communication, for example via RS-232 or USB links. Nine bit binary
is reserved for the 10 Mbit/s fiber-optic channel, and is highly recommended for larger systems
with multiple addressable devices in a loop.
F100 User Manual
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