SN74AVC4T245: Direction error

Sriram A

Part Number: SN74AVC4T245
Other Parts Discussed in Thread: SN74AXC4T245

please find the below image. i have my schematic as well as directions of module. i think there is a mistake in level converters direction configuration. please help me make the changes

over 5 years ago

0 Clemens Ladisch over 5 years ago

Guru 316690 points

1DIR is high, so the direction is 1A1→1B1 and 1A2→1B2.
2DIR is low, so the direction is 2B1→2A1 and 2B2→2A2.

So the RX and CTS signals go from 1.8 V to 3.3 V, and the TX and RTS signals go from 3.3 V to 1.8 V. This appears to be correct.

0 ShreyasRao over 5 years ago

TI__Guru 62050 points

Sriram,

You could also consider using the SN74AXC4T245 which is more robust and P2P with the AVC4T245.

0 Sriram A over 5 years ago in reply to Clemens Ladisch

Prodigy 40 points

the net name GSM_RX and GSM_CTS are supposed to be input to 1.8V. please refer 2nd image. i need to change the direction.

1B1-->1A1 & 1B2-->1A2

2A1-->2B1 & 2A2-->2B2

0 Clemens Ladisch over 5 years ago in reply to Sriram A

Guru 316690 points

What are the voltages of GSM_xxx and MCU_xxx? Which one is DCE or DTE?

0 Sriram A over 5 years ago in reply to Clemens Ladisch

Prodigy 40 points

GSM_xxx is 1.8V & MCU_xxx is 3.3V.

GSM is DCE, MCU is DTE

0 Clemens Ladisch over 5 years ago in reply to Sriram A

Guru 316690 points

Everything looks correct.

Why exactly do you think that the direction is wrong?

0 Sriram A over 5 years ago in reply to Clemens Ladisch

Prodigy 40 points

second image is correct. but please look at the schematic that i used. it is wrong.

0 Clemens Ladisch over 5 years ago in reply to Sriram A

Guru 316690 points

The A port is the 1.8 V GSM side. The B port is the 3.3 V MCU side.

RXD and CTS go from 1.8 V to 3.3 V, i.e., from A to B.

The 1DIR pin is pulled high, which means A→B, which is correct.

What exactly do you think is wrong?

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SN74AVC4T245: Direction error