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1.1 INTRODUCTION
This document describes the use of two RS422_RS32 Protocol Interface Translators
(PIT) in order to extend the connection of intercom control keyboards. The
interconnection between the PITs uses a standard RS232 communications channel.
Data activity on the RS232 channel is kept to a minimum.
The PIT, which connects to the VideoBloX intercom CPU, simulates a keyboard. This PIT
will be referred to as the Intercom CPU PIT. It receives LED control message packets on
its RS422 slave port and converts these into single ASCII characters in the range 'A'..'X'.
These characters are then transmitted out of the RS232 master port. ASCII characters in
the range '0'..'7' received on the RS232 port simulate key presses on the intercom
keyboard and are stored in a buffer. When the Intercom CPU reads the PIT, the
corresponding key code is returned.
The PIT which connects to the remote keyboard polls the Intercom keyboard via it's
RS422 Slave port. This PIT will be referred to as the keyboard PIT. When it detects any
key press, these are converted into ASCII characters in the range '0'..'7' which are
transmitted out of the RS232 master port. ASCII characters in the range 'A'..'X' received
on the RS232 port are converted into LED control packets and sent to the keyboard.
Rev. 1
1
900.0405
23-June-05
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