I have a quick question about UART communication between the AT89S52 and my laptop.

I’m trying to send data from the AT89S52 over UART, and I know there are different interface standards like TTL and RS232. I plan to use a CP2102 USB-to-TTL converter for this.

Now, the AT89S52 runs on 5V, and I saw that the CP2102 uses 3.3V logic levels (even though its VCC can be 5V).

I’m attaching the links to both the CP2102 module and the AT89S52 MCU below for reference:

Link to CP2102 module https://robu.in/product/cp-2102-6-pin/?msclkid=67f1bcb79bb2153ec917dbceaca34145

Link to AT89S52 datasheet https://ww1.microchip.com/downloads/en/DeviceDoc/doc1919.pdf

So I’m wondering will CP2102 communicate properly with the 5V AT89S52? More specifically, will the 5V TX from the AT89S52 damage the 3.3V RX pin on the CP2102, or is it safe to connect directly?

Just wanted to be sure before I hook it up. Thanks

 

I have a quick question about UART communication between the AT89S52 and my laptop.

I’m trying to send data from the AT89S52 over UART, and I know there are different interface standards like TTL and RS232. I plan to use a CP2102 USB-to-TTL converter for this.

Now, the AT89S52 runs on 5V, and I saw that the CP2102 uses 3.3V logic levels (even though its VCC can be 5V).

I’m attaching the links to both the CP2102 module and the AT89S52 MCU below for reference:

Link to CP2102 module https://robu.in/product/cp-2102-6-pin/?msclkid=67f1bcb79bb2153ec917dbceaca34145

Link to AT89S52 datasheet https://ww1.microchip.com/downloads/en/DeviceDoc/doc1919.pdf

So I’m wondering will CP2102 communicate properly with the 5V AT89S52? More specifically, will the 5V TX from the AT89S52 damage the 3.3V RX pin on the CP2102, or is it safe to connect directly?

Just wanted to be sure before I hook it up. Thanks

3.3V will be above the Vih threshold for the processor, so the input to the processor will be OK.
5V will damage the interface unless it says it has 5V tolerant inputs.
if it hasn’t attenuate the signal with 1.2k in series and 2.2k to ground.

 

3.3V will be above the Vih threshold for the processor, so the input to the processor will be OK.
5V will damage the interface unless it says it has 5V tolerant inputs.
if it hasn’t attenuate the signal with 1.2k in series and 2.2k to ground.

Thanks for the explanation! So, if I understood correctly:

The CP2102 TX (3.3V) going into the AT89S52 RX is fine because 3.3V is above the AT89S52’s (Input High Voltage) threshold. So, the AT89S52 will recognize it as a logic high — no problem there.

But the AT89S52 TX (5V) going into the CP2102 RX (which uses 3.3V logic) could damage the CP2102

To be safe, I should drop the 5V signal going to the CP2102 using a voltage divider 1.2kΩ in series and 2.2kΩ to ground which brings it down to around 3.3V.

One more thing: I’m not able to find the exact circuit diagram of the CP2102 module I have, so I’m not sure whether its RX pin is 5V tolerant or not.

That’s why I’m a bit confused. can I connect it directly to the AT89S52, or should I use the voltage divider (like the 1.2k and 2.2k resistor combination you mentioned)?

Just want to be sure before making any connections. Let me know if I’ve got it right!

 

Thanks for the explanation! So, if I understood correctly:

The CP2102 TX (3.3V) going into the AT89S52 RX is fine because 3.3V is above the AT89S52’s (Input High Voltage) threshold. So, the AT89S52 will recognize it as a logic high — no problem there.

But the AT89S52 TX (5V) going into the CP2102 RX (which uses 3.3V logic) could damage the CP2102

To be safe, I should drop the 5V signal going to the CP2102 using a voltage divider 1.2kΩ in series and 2.2kΩ to ground which brings it down to around 3.3V.

One more thing: I’m not able to find the exact circuit diagram of the CP2102 module I have, so I’m not sure whether its RX pin is 5V tolerant or not.

That’s why I’m a bit confused. can I connect it directly to the AT89S52, or should I use the voltage divider (like the 1.2k and 2.2k resistor combination you mentioned)?

Just want to be sure before making any connections. Let me know if I’ve got it right!

Just because it is 5V tolerant shouldn’t encourage you to connect 5V to it. Attenuate it to3.3V, for the sake of good practice.

 

Just because it is 5V tolerant shouldn’t encourage you to connect 5V to it. Attenuate it to3.3V, for the sake of good practice.

Thanks for the clarification!

So I’ll use the voltage divider (1.2k + 2.2k) to bring the AT89S52 TX down to 3.3V before connecting it to the CP2102 RX.

 

The CP2102 chip has a maximum rating of 5.8V on any I/O pin, even though Vdd for the chip is in the 3.3V range. That is, I/O is TTL compatible, where TTL is defined as 5V levels.
I've used CP2102 modules with regular 5V arduinos with no issues.