The 1784-PCMC4 cable for PCMK-DH485 has an RJ45 port in the DH485-end, and looks like this:
http://www.***********.com/prodimg/RA-1784-PCM4-B-UPP.jpg
DO NOT PLUG IT INTO THE RJ45 PORT ON THE L551 CPU !
In order to connect from the PC to the L551 CPU by means of the PCMK & PCMC4, there must be a 1747-AIC in between, and a 1747-C11 cable from the AIC to the CH0 port on the L551. Like in this post:
http://www.plctalk.net/qanda/showpost.php?p=207859&postcount=7
(edit: Thinking again, I think it is wrong. You can go from an AIC to an L531, but not to a L551).
All this assumes the CH0 port is setup for DH485 which is not unlikely. I aggree with OkiePC that you should post the program.
If the CPU has completely lost the program, you should try to connect to it via plain serial DF1.
That requires a null-modem cable from a serial port on the PC to the CH0 port on the L551.
In RSLinx setup a "RS-232 serial DF1" device. Set "device" to "SLC-CH0/Micro/Panelview" and hit the "Auto-configure" button. If it connects and the detected baudrate is 1200, then it is almost certain that the program has been lost.
http://www.***********.com/prodimg/RA-1784-PCM4-B-UPP.jpg
DO NOT PLUG IT INTO THE RJ45 PORT ON THE L551 CPU !
http://www.plctalk.net/qanda/showpost.php?p=207859&postcount=7
All this assumes the CH0 port is setup for DH485 which is not unlikely. I aggree with OkiePC that you should post the program.
If the CPU has completely lost the program, you should try to connect to it via plain serial DF1.
That requires a null-modem cable from a serial port on the PC to the CH0 port on the L551.
In RSLinx setup a "RS-232 serial DF1" device. Set "device" to "SLC-CH0/Micro/Panelview" and hit the "Auto-configure" button. If it connects and the detected baudrate is 1200, then it is almost certain that the program has been lost.
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