CY545 Stepper System Controller
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F = 9600 baud
1 = 2400 baud
0 = 300 baud
When the IO_REQUEST line is left floating, 9600 baud is selected. When tied high, 2400 baud
is selected, and when tied low, 300 baud is selected. For these fixed rates to be correct, the
CY545 must be operated with an 11 MHz crystal clock. Other values will scale the baud rate
linearly by the difference in crystal frequencies.
An alternative method of selecting the baud rate is through a parallel Mode command. For this
command, nine baud rate selections are available, from 300 to 57600, plus the self adaptive
rate. Details of the Mode command are described in a later section.
Note that the selection of fixed baud rate mode through the BUSY and IO_REQUEST lines,
gives up the use of the parallel handshake interface, since the lines are used to select the baud
rate. This is fine if only the serial interface will be used. However, if both interfaces must be
used on the same CY545, the baud rate may only be set adaptively, or through a parallel Mode
command.
The adaptive serial mode is chosen by default, when the BUSY signal is left floating, so the
CY545 can drive it at power up. In this mode, the serial baud rate is not set until the CY545
receives two carriage return codes. Be sure to send these characters after power up or any
reset (hardware or software). Once the two carriage returns have been received, normal CY545
commands may be sent.
When working with the serial interface, the best crystal frequency for the CY545 is 11 MHz. This
will provide the largest baud rate operating range, with the least baud rate error. Internal timer
resolution of the CY545 will limit the available rates, especially at the high end. At 11 MHz,
standard rates up to 19200 baud may be selected. Note that other CY545 functions, such as the
step rates and time delays, have been calibrated for a 12 MHz clock source. This means these
functions will run somewhat slower when 11 MHz is used. Changes to the relevant parameter
values can compensate for some of this difference. Alternatively, a 12 MHz clock will work fine,
if the selected adaptive baud rates are always 4800 baud or less.
When operating the CY545 at 16 MHz, internal timer resolution still limits the reliable operation
of the serial interface to 4800 baud or less. The error at higher baud rates may be too great for
consistent communications.
© 2002 Cybernetic Micro Systems
13
Chapter 3 - Command Interfaces
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