MDB (Multi-Drop Bus) polling request always returns 0x0b while everything else works fine

Thread Starter

ElazarM

Joined Aug 10, 2021
3
I am developing an MDB (Multi-Drop Bus) driver for a coin changer for Arduino ESP32 - MDB Protocol Documentation: PDF Link.

I am testing my code with an MEI CF 7000 Coin Changer.

I have tested all commands, and everything seems to respond correctly (according to the protocols documentation)

However, the only (but necessary) thing I don't understand is that whenever I send a POLL request (0x0b), it always returns 0x0b.
The device returns 0x0b while fully configured and working as expected; it accepts and dispatches coins when asked to.

Question: When sending a POLL command, why does the device always return 0x0b even when it does not seem to be in the reset mode?

I have tested this with two different devices, and both give me the same results!
This means that there is something that I am missing or that I do not understand how the polling request works.
 

Thread Starter

ElazarM

Joined Aug 10, 2021
3
I am developing an MDB (Multi-Drop Bus) driver for a coin changer for Arduino ESP32 - MDB Protocol Documentation: PDF Link.

I am testing my code with an MEI CF 7000 Coin Changer.

I have tested all commands, and everything seems to respond correctly (according to the protocols documentation)

However, the only (but necessary) thing I don't understand is that whenever I send a POLL request (0x0b), it always returns 0x0b.
The device returns 0x0b while fully configured and working as expected; it accepts and dispatches coins when asked to.

Question: When sending a POLL command, why does the device always return 0x0b even when it does not seem to be in the reset mode?

I have tested this with two different devices, and both give me the same results!
This means that there is something that I am missing or that I do not understand how the polling request works.
In the end, I figured it out! The Master didn't send a correct ACK after receiving data from the slave (the coin changer); once I fixed this, it started to work as expected!
 

jiggermole

Joined Jul 29, 2016
161
thank you. there are a number of times ive seen questions im interested in and the original poster has solved it but never came back and let us know that they have. Its good to see it when it does happen.
 

mikeme

Joined Jan 22, 2019
1
Hi ElazarM. I have an undergraduate project with esp32 and MDB bill validator. I can not communicate with the bill validator. I used a logic analyzer to see a working communication, but when I send the same command (0x130 0x30) to bill validator, does not respond. Esp32 and bill validator connect directly RX-TX and TX-RX or do I need to add adapters with an integrated HEX inverter? Can you help me with some tips?
 
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