Controller - Institute of Transportation Engineers

4.3.5.4 One KHz Reference
A synchronizable 1 KHz time reference shall be provided. It shall maintain a frequency
accuracy of ±0.01% (±0.1 counts per second).
4.3.5.5
A 32-bit MILLISECOND COUNTER (MC) shall be provided for “timestamping.” Each
1 KHz reference interrupt shall increment the MC.
4.3.5.6
At Power Up, the FCU loss of communications timer shall indicate loss of
communications until the user program sends the Request Module Status message to reset
the “E” Bit and a subsequent set output command is processed.
4.3.5.7
A LOGIC Switch shall be provided resident on the module board. The switch shall
function to disconnect Serial Port 3 ( SP3) from the external world, Connector C12S. Its
purpose is to prevent multiple use of SP3. A LED shall be provided on the module front
panel labeled “SP3 ON”. If LED light ON, SP3 is active and available at C12S.
4.3.6 Serial Communications/Logic Circuitry
4.3.6.1
System Serial Port 5 (SP5) EIA-485 signal lines shall enter the I/O Module and be split
into two multi-drop isolated ports. One shall be routed to the FCU and the other
converted to EIA-485, then routed to Connector C12S.
4.3.6.2
System Serial Port 3 (SP3) EIA-485 signal lines shall enter the I/O module and be
isolated, converted back to EIA-485 and then routed to connector C12S.
4.3.6.3
LINE SYNC and POWER DOWN lines shall be split and isolated, one routed to the FCU
for shut down functions and the other changed to EIA-485; then routed to connector
C12S for external module use.
Standard for the ATC – Type 2070 March 29, 2001
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