TRSF3221E: Junk Output Values

Hi Nachiketh,

So to clarify - the transceiver console side outputs aren't good  (ROUT) - but the bus inputs to the transceiver are (RIN) am I correct in my understanding? 

If that is the case - can you share the input and output signals in a scope shot - preferably both input and output on the same screen - one on each channel.

Also have you probed the /INVALID pin to see if there is any issue with the data being received?  If so - what value is it (high or low?) 

Also how long is your bus between driver and receiver ? 

Please let me know so I can dig into this issue a bit deeper for you.

Best,

Parker Dodson

Hi Parker,

Yes the transceiver console outputs aren't good, but the inputs are.

I have attached the scope shot of Rin, Rout and Din, Dout.

Invalid pin is high.

What do you mean by distance between driver and receiver, I did not get you.

Regards,

Nachiketh

/cfs-file/__key/communityserver-discussions-components-files/138/tek0123.tif

/cfs-file/__key/communityserver-discussions-components-files/138/tek0124.tif

INVALID: 01001001 01001110 01010110 01000001 01001100 01001001 01000100
IHDAHID: 01001001 01001000 01000100 01000001 01001000 01001001 01000100

Only some bits are wrong. Please show the DOUT signal for at least an entire byte; preferrably at the place where the wrong value is received.

Are the capacitors near the chip? Please show the board layout.

Hi Clemens,

I have attached the board layout.

Regards,

Nachiketh

/resized-image/__size/320x240/__key/communityserver-discussions-components-files/138/Screenshot-2023_2D00_03_2D00_29-191947.png

Hi Nachiketh,

Can you show the DOUT and ROUT waveform for the entire bit string - especially where the values are received as wrong? 

As the output looks fine, the /INVALID pin being high also shows that the device is receiving valid data as well. I don't know if this is a transceiver problem directly - but I want to see the entire bit stream  as that could help indicate any issues in the signal at that point.

For the length of the bus - essentially how long is the cable/trace between the output of the transceiver (DOUT) to the receiver input (RIN) - RS-232 maxes out at ~15m (2500pF loading is the spec - which typically is about 15m of cable) - so I just wanted  to better understand the bus to see if there is an issue there. I don't think so based what has been shown so far - but seeing the entire bit stream will help determine if the signal is the issue. 

If the signal that I am requesting looks clean - I don't think the issue is the transceiver - it could be layout and or controller issues, but please if you can provide that scope shot of the entire bitstream I should be able to see if there are any potential issues with the transceiver itself.

Best,

Parker Dodson 

Hi Parker,

1. I have attached both DOUT and ROUT bit strings. ROUT default state is low. When we press any key there is a change in the waveform. The attached snap is a scope shot after pressing the enter key.

/cfs-file/__key/communityserver-discussions-components-files/138/tek0155.tif

/cfs-file/__key/communityserver-discussions-components-files/138/tek0157.tif

/cfs-file/__key/communityserver-discussions-components-files/138/tek0158.tif

2. Trace length of DOUT is 17.72mm and RIN is 17.63mm . The length of cable used to connect to DOUT and RIN is 1m. Part number of cable used is

TTL-232R-3V3

3. I have attached the board layout.

/cfs-file/__key/communityserver-discussions-components-files/138/RS232_5F00_IN_5F00_and_5F00_OUT_2D00_30_2D00_03_2D00_23.brd

Regards,

Nachiketh

The two DOUT voltage levels should be near −5.4 V and 5.4 V. Apparently, the negative charge pump does not work correctly. What is the voltage at the V− pin? Can you check if both C1 and C2 are switching voltages?

Hi Nachiketh,

Thanks for the additional scope shots.

I agree with Clemens - the DOUT low level seems to be too high - which could be causing some issues on data reception (which could explain the junk values you are receiving).

Can you measure the V- to see what voltage level is present on this pin - as it should be at ~ -5.4V. 

If it isn't - can you possibly test one other device and see if the issue is there also.

Could you share the part markings on top of the IC package as well?

I want to trace to the lot information 

Best,

Parker Dodson 

Hi Parker and Clemens,

1. I observed voltage at pin V- to be -3.5V, I have attached the scope shot for your reference.

/cfs-file/__key/communityserver-discussions-components-files/138/tek0166.tif 

2. I have attached the scope shot at points C1 and C2.

/cfs-file/__key/communityserver-discussions-components-files/138/tek0172.tif

/cfs-file/__key/communityserver-discussions-components-files/138/tek0171.tif

3. I tried testing with other device, but still facing the same issue. I have attached the part marking on top of IC package.

/resized-image/__size/320x240/__key/communityserver-discussions-components-files/138/1680243418145.JPEG

4. Do you see any issue in the layout design?

Regards,

Nachiketh

The layout and the C1/C2 curves look OK; this does not appear to be a problem with the TRSF itself.

The low DOUT level is about −0.7 V, which is a diode drop. Might it be possible that there is a diode between DOUT and ground? Is there a protection diode somewhere? Please show a schematic that includes everything connected to DOUT.

Hi Clemens,

1. There is no diode between DOUT and ground, also there is no protection diode anywhere.

2. I have attached the schematics with everything connected to DOUT.

/resized-image/__size/320x240/__key/communityserver-discussions-components-files/138/Screenshot-2023_2D00_03_2D00_31-125319.png

3. Is the voltage at pin V- correct? Shouldn't it be ~ -5.4V?

Regards,

Nachiketh

Hi Clemens,

1. I have attached the schematics with everything connected to DOUT.

/cfs-file/__key/communityserver-discussions-components-files/138/Schematics1.pdf

Regards,

Nachiketh

Do you get the same output voltage when the TTL-232R-3V3 cable is not connected?

Hi Clemens,

I observed the same voltages when TTL-232R-3V3 cable is not connected. I have attached the scope shot.

/cfs-file/__key/communityserver-discussions-components-files/138/tek0175.tif

Regards,

Nachiketh

Without the cable, the voltages are OK. (Note that the negative voltage goes beyond −5 V.)

So I have to conclude that this cable has some error. Do you have its schematic?

Hi Nachiketh,

As Clemens has mentioned - it does seem to be a possible cabling issue.

1. Do you have the part number for the cable so I can look into its specifications.

2. Is it possible to replace the cable (even of the same kind) to test to see if it may just be the individual cable

Everything else from the transceiver looks okay.

Please let me know.

Best,

Parker Dodson

Hi Parker and Clemens,

1. Part number of the cable used is TTL-232R-3V3.

2. Tried replacing cable of same kind but still the issue persists.

3. I have attached the datasheet of the cable.

/cfs-file/__key/communityserver-discussions-components-files/138/DS_5F00_TTL_2D00_232R_5F00_CABLES.pdf

Regards,

Nachiketh

Hi Clemens,

1. If  TTL-232R-3V3 cable cannot be used, what might be an alternate cable that can be used for testing.

2. I have also tried with a cable which has DB-9 male connector connected to one end and 100mil berghouse connector to be connected to the board in the other end, but i did not even get junk values this time, although the DOUT voltage was ~-5.6V.

Regards,

Nachiketh