TRS3243E: Loopback doesn't work

Kiran Munj

Part Number: TRS3243E

Tool/software:

I connected my USB into laptop.

I have opened a tera terminal and loopback (Jumper) between TxD (Pin #6) and RxD (Pin #1) pins.

When I enter any key from my laptop, I don't see any response. I should get the character back on my screen like other FTDI RS-232 cable does.

I have FORCEON (Pin #22) connected to GND and /FORCEOFF (Pin #21) connected to +5V.

Why this simple loopback doesn't work?

Thanks

Kiran

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 317480 points

The pin numbers are not correct for the TRS3243E; see section 5 of the datasheet.

0 Ethan Sempsrott over 1 year ago

TI__Genius 14412 points

Hi Kiran,

Please confirm your specific package for TRS3243E. If you have the VQFN (32 pin) package, then your pin numbers are correct. If you are using SSOP, SOIC, TSSOP (28 pin), then you do indeed have the wrong pinout.

If your pin numbers are correct and you are still having trouble, please send a schematic of the device for verification.

Best,

Ethan

0 Kiran Munj over 1 year ago in reply to Ethan Sempsrott

Intellectual 520 points

We are using VQFN (32 pin) package. The board works when connected to the end device (e.g. serial modem). But if I disconnect the end device and put a loopback, loopback test does not work.SCH_1061506-01_R3.3.PDF

Attached is the schematic.

Thanks

Kiran

0 Kiran Munj over 1 year ago in reply to Kiran Munj

Intellectual 520 points

i also connected U2-22 (FORCEON) to GND and loopback still did not work.

Thanks

Kiran

0 Clemens Ladisch over 1 year ago in reply to Kiran Munj

Guru 317480 points

Sorry for the QFN oversight.

In the schematic, FORCEON is floating; this is forbidden.

When FORCEON is low, then the transceiver is automatically powered off and powers on only when it detects a valid RS-232 signal from the device at the other end of the bus (i.e., it expects the other device to never power down). This does not work in a loopback configuration.

For this test, you have to pull FORCEON high.

0 Ethan Sempsrott over 1 year ago in reply to Clemens Ladisch

TI__Genius 14412 points

I agree with Clemens. The floating FORCEON is the issue for running the loopback test. Keep it high for this scenario. Section 8.3 of the datasheet further describes the FORCEON/OFF configurations:

Let us know if you have any other questions,

-Ethan

0 Kiran Munj over 1 year ago in reply to Ethan Sempsrott

Intellectual 520 points

Thank you very much for your help. I got loopback to work when I connected FORCEON (Pin 22) to +5V.

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TRS3243E: Loopback doesn't work