CY545 Stepper System Controller
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CHAPTER 16 - TIMING AND CONTROL
Timing and Control
This section contains more detailed timing and applications information for various signal groups
of the CY545. Included are the command interfaces, special external hardware support, and
motor control signals.
The Parallel Handshake
The CY545 parallel command interface uses three control signals, plus the data bus lines for
actual data transfers. The control signals are IO_REQUEST, BUSY, and FPL, which is a shared
function with USRB6. IO_REQUEST is an input, driven by the device sending commands to the
CY545, while BUSY and FPL are outputs, indicating status of the CY545.
The IO_REQUEST signal is used to control the parallel handshake functions, The signal is
normally high when no commands are being sent to the CY545. To issue commands, wait until
the BUSY line is high, indicating that the CY545 is ready for commands, then put a command
byte on the data bus lines, and drive IO_REQUEST low. Keep the data signals and
IO_REQUEST stable until the CY545 responds by driving BUSY low. Note the response time is
normally around 25 microseconds (usec), so the CY545 is slower than an I/O peripheral or
memory device, and some systems may require a latch on the data bus signals. Once the
BUSY signal has gone low, the IO_REQUEST signal should be driven high again, and the data
signals may be removed. A typical handshake waveform is shown below.
Every command character must be sent to the CY545 with the above described handshake.
Timing for the handshake will vary somewhat, and the CY545 will go busy for longer periods of
time after the last character of a command is issued. This represents the actual execution time
of the command.
When the command is a query command, the CY545 will generate a response to the query as
part of the command execution. If the mode register is set so that query responses come out the
standard parallel interface (MB0 = 1 and MB2 = 0), a handshake will also be used for the data
generated by the CY545. In this case, the CY545 will drive the FPL signal low to indicate that it
© 2002 Cybernetic Micro Systems
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Chapter 16 - Timing and Control
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