SN75176A/B Issue

Alfred Logico

Expert 5380 points

Other Parts Discussed in Thread: SN75176A, SN75176B

Hi Team,

Good day!

One of my customers faced an issue using our SN75176 for their RS485 communications.

Here’s the summary of the issue that they were encountering with the SN75176:

Master:

· Baudrate: 115200
· RE Pin: Tied to GND
· DE Pin: Tied to VDD

Slave:

· Baudrate: 115200
· RE Pin: Controlled by MCU
· DE Pin: Controlled by MCU

Master

Slave

Remarks

SN75176A

Master cannot receive correctly from the slave.

Slave can receive data from the master correctly.

SN75176B

Doesn’t communicate correctly.

Here is also the schamtic of their master and slave:

Master

Slave

Please help advise on what can cause this issue?

Thanks!

Regards,

Alfred

over 9 years ago

0 Ron Michallick over 9 years ago

TI__Guru**** 171336 points

Alfred,

Communication between any combination of SN75176A and SN75176B should work well.
Can you try attaching schematic again? I see only blank images.

0 Alfred Logico over 9 years ago in reply to Ron Michallick

TI__Expert 5380 points

Hi Ron,

I am reattaching the pictures below:

MASTER

SLAVE:

Thanks!

Best Regards,

Alfred

0 Ron Michallick over 9 years ago in reply to Alfred Logico

TI__Guru**** 171336 points

Alfred,

The most likely problem is the 1k and 0.01uF capacitors on the master's logic side.
The RC delay is too long for 115200 data rate.
The 1k resistor may cause the low logic level voltage input to be too high and unreliable.

Interface

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SN75176A/B Issue