CY545 Stepper System Controller
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However, the CY545 will also accept another form of parameter for the arguments of the
commands. This form replaces the numeric argument with a “#” character, and it means to
read the actual parameter value from an external source, normally implemented as thumbwheel
switches. Only the first parameter of a command with multiple parameters may be read this
way, but this is not a severe restriction, since the second parameter is usually a branch address,
and could be fixed anyway. Programs may repeat things a variable number of times, but usually
go to the same place in the loop. Examples of this new format are shown below:
R #<cr>
Get Rate value from thumbwheels
Get Number of steps from thumbwheels
Get Loop repeat count from thumbwheels
N #<cr>
L #,123<cr>
In all cases, the format for the command is identical to that with the numeric arguments, except
that the numbers are replaced by the “#” character. Note that this format only works in the ASCII
command mode, since the “#” character cannot be distinguished from a valid parameter byte
value in the Binary command mode. All other characters of the command stay intact, including
the space after the command letter, comma or space between arguments, and carriage return
at the end of the command.
When these commands are written to external memory, the “#” character is included in the
memory contents. Recall that the external memory contents are identical to the characters sent
in the direct command mode. The CY545 will act on the character, and read the parameter
value every time the program is run, and a command containing the “#” character is read.
When the “#” character is processed by the CY545, it generates a special read sequence to get
the value of the parameter from the external switches. Each parameter consists of 3, 5 or 8
digits, depending on whether the parameter is a byte or two byte size. Each parameter is
assigned an address range of 3, 5, or 8 addresses, generated on the lower byte of the two
address latches, controlled by the ALE signal.
In order to read a specific digit, the CY545 generates the digit address, latched into the lower
address byte latch. It then generates a RD strobe, with the SW_SEL line low. This should
enable the data from the addressed switch onto the CY545 data bus. All switches are positive
BCD encoded. The CY545 reads the switch value from the lower four bits of the data bus, then
converts the value into an ASCII decimal digit. The hex format is not supported for externally
read parameter values.
© 2002 Cybernetic Micro Systems
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Chapter 13 - Thumbwheel Switch Support
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