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Walkthrough Wednesdays

DMP-4400, rs232 commands not being sent to device

Recently we had deployed 16 DMP-4400 attached to televisions in our environment. All of them are configured identically, and have the same model of TVs attached to them. Four of them refuse to pass rs232 commands to the attached TVs, and are much slower to load the content to be displayed, a significant difference in loading time.  Disabling the rs232 allows the content to load at a normal speed.

I have replaced the rs232 cables, wiped out the configuration and reconfigured.

The rs232 is being enabled with the following command:


Firmware version 5.2.3

The rs232 parameters from the DMP:

rs232.device          T_STRING          /dev/ttyS0

rs232.speed          T_STRING          9600

rs232.parity          T_STRING          none

rs232.data_size          T_STRING          8

rs232.stop_bits          T_STRING          1

rs232.flow_ctrl          T_STRING          none

rs232.tx_hex          T_STRING

rs232.tx_str          T_STRING

rs232.rx_buf          T_STRING

rs232.rx_overflow_flag          T_STRING          false

rs232.tx_cnt          T_STRING          0

rs232.rx_cnt          T_STRING          0

When sending a command the rs232.tx_hex string should populate, and the rs232.tx_cnt should increase in value, these values never change. The commands are being sent from DMM version 5.3 and work on the 12 other DMPs that are in place.  Connecting a rs232 sniffer also shows that nothing was sent from the DMP.

Anyone have any ideas?


Check your RS232 Cables.

You only need Pin 2,3,5  any others will cause com issues.

Had same problem with a Samsung monitor and a DMP4400.

It connected pins 7,8 which were causing the problem.

When you were having the issues with the Samsung monitor, was this also causing the content loaded on the screen to load at a extremely slow rate, or where you just experiencing issues with the rs232 commands?  Currently even when the rs232 cable is removed the content loads at a slower rate with rs232 enabled, disabling it causes the DMP to preform as expected.

Yes , The content would play back slow as long as the cable was atached.

It acted like it was tying up the com port and  caused the content to be slow and step .


Hi David, I am encountering a similar problem now when connecting RS232 cables to DMP 4400 on 5.2.3. The DMP CPU will spike to 100% whenever the R2232 cable is connected to the DMP. Will like to find out whether you eventually found a solution to the problem? Does removing other pins on the connector other than pins 2, 3 and 5 helped?

Thanks in advance!

It seems impossible to purchase RS232 cables with the correct pinout, everyone sales the cable with "RS232 null modem with full handshaking".  For this you need the "Simple RS232 null modem without handshaking", which only uses the 3 pins, 2, 3, and 5.

I ended up making my own cables, using RJ-45 to DB9 Adapters, and pinning them myself. Flipping TX and RX on one end, after this everything worked as expected.

Thanks for your reply! Hopefully I can get the ones without handshaking from the shop, dread the idea of having to make my own cables :)

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