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3.8 MMI Response
The MMI is limited in its response to key presses and information update by the
serial communications to the PLC. The MMI has been optimized to provide reason-
able response times to events.
3.8.1 Response Time to Message Calls, LED, Beeper and O.C.
Output Activation
A message number must be in the MTR or bit sequence change in the LED
register for at least 300 milliseconds to be recognized by the MMI.
3.8.2 Response Time to Function Key Presses
Function keys are handled on an interrupt basis. As soon as a key is
pressed, a communication is sent to the PLC. Response to a key press by
the PLC depends on the PLC’s scan time and communications handling.
Typically, response times are less than 1 second. We do not recommend
using the function keys for JOGGING applications.
3.8.3 Response Time to Serial Port Transmissions
MMI-220, 240
When a called message has the attribute to be sent to the serial
port, the MMI-2XX will send the message to the port before
displaying it. Response time is determined by the number of
registers/bits embedded in the message. The serial port baudrate
also determines how long it will be before the message is dis-
played. A 200 character scrolling message with several embedded
registers and bits sent out at 300 baud may take up to 10 sec-
onds to appear on the display.
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