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CY545 Stepper System Controller

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wants to generate some output to the parallel interface. The CY545 then waits for the

IO_REQUEST signal to go low, indicating that the host system is ready for data. The data byte

is written to the data bus, and the BUSY signal is driven low. This indicates that data is available

to the host. When the host drives the IO_REQUEST signal high again, the bus is cleared, and

BUSY is brought back high also.

In the ASCII command mode, the FPL signal will continue to stay low as long as the CY545 has

data to generate. This is an indication that the host should continue reading data bytes from the

CY545. The FPL signal will be brought high when the CY545 writes a carriage return code,

indicating the end of the response.

In the Binary command mode, data may have any value, so each byte sent out will toggle the

FPL line back high again. When there are multiple bytes to send, the FPL signal will be brought

low as the CY545 is ready to generate the next data byte value.

This behavior is compatible with the CY233 LINC device, generating one message for query

responses in the ASCII mode, and one message per data byte in the Binary mode. A typical

query response waveform is shown below.

Immediate Commands

During External Memory Program Execution

The CY545B supports the acceptance and proper execution of immediate commands while

executing a program from external memory. However, the handshakes for this function are a

little more complex than the standard command handshake. More details are provided in this

section.

The FPL signal is very important in implementing the handshake protocol for immediate

commands, especially if the CY545 is also generating query responses or quoted messages

from the local memory program.

The FPL signal, driven by the CY545, can be used to control the direction of data on the CY545

local data bus. When FPL is high, the CY545 can accept command inputs, and when FPL is

low, the CY545 has output data for the parallel host.

© 2002 Cybernetic Micro Systems

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Chapter 16 - Timing and Control