Owners Manual
2800 Series Marquee
1.10 Setting the U3 Message Memory Chip Type (J1)
The J1 option jumpers are used to configure the processor board U3 message memory socket for different types
of chips. In most cases, U3 will be populated with a 28C64 (64K x 8 EEPROM) chip, and all four J1 positions (A,
B, C, and D) should be left open as shown in the picture. However if you have a special memory chip installed in
your processor board, the factory will install J1 jumpers as required before shipment. Please do not change the
J1 jumper settings without contacting American LED-gible technical support first.
1.11 Connecting the RS-485 Transmitter (J2)
The J2 option jumpers are used to connect the AB-2476-020 RS-485 transmitter to the serial communications
connector. Installing the J2 jumpers allows the marquee to send data back to the PC/PLC over the same RS-485
wires that the PC/PLC uses to send data to the marquee(s). However, if a marquee and the PC/PLC try to send
data at the same time, the RS-485 packets collide and are destroyed. When the J2 jumpers are installed, it is the
PC/PLC programmers responsibility to provided the marquee(s) with sufficient time to respond to requests.
Doing so prevents RS-485 packet collisions from occurring.
Alternately, removing the J2 jumpers disconnects the AB-2476-020 RS-485 transmitter from the serial
communications connector. This prevents the marquee from sending data back to the PC/PLC via RS-485, but it
also makes it impossible for the marquee to send a packet that collides with packets being sent by the PC/PLC.
In most cases the J2 jumpers should not be installed because the PC/PLC is only sending data to the marquee(s)
and is not interested in retrieving data from the marquee(s).
NOTE: Removing the J2 jumpers does not prevent the marquee from sending data back to the PC/PLC if RS-232
full duplex wiring is used. RS-232 uses separate wires for data traveling in each direction.
PB-2149-335B Page 9
(12 Seiten)
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