Which type of communication used in system? - Page 1
Forum section: electronics / general

author: natiz
author_rank: Newbie
timestamp: September 02, 2019, 09:18:07 pm
content: I have this really old alarm system, and I want to be able to get the output of its sensors using an ardunio/nodemcu.The main board has anAmtel TS80C51RA2-MCAand aM27C4001EPROM.The expansion boards and keypads that connect to it are all using this '4-wire bus' and have a (DIP to choose their ID), and I'm trying to figure out which comm. protocol they use.I initially thought it was i2c, since you can hook all of them up and give each one an 'ID', but I don't think the MCU supports it?I posted some images of the manual/expansion board.Any thoughts on how to figure this one out?

author: mikerj
author_rank: Super Contributor
timestamp: September 02, 2019, 09:31:35 pm
content: Are there any driver ICs between the micro and the bus?

author: lucazader
author_rank: Regular Contributor
timestamp: September 02, 2019, 09:32:04 pm
content: Could be half duplex SPI?Or an addressed uart/rs232/rs485.

author: mjs
author_rank: Regular Contributor
timestamp: September 03, 2019, 07:46:54 am
content: I've seen RS485 and custom clock+data (DSC) and Wiegand derivatives. Red/Black is for power, green/yellow for bus data.Scope it with small (10ohms) resistors in series betwen the central unit and sensors/keyboards to be able to see signals and who's driving the signal.Here's a discussion about the DSC communcations, which might be close to that:https://www.avrfreaks.net/forum/dsc-keybus-protocol?page=all

author: nctnico
author_rank: Super Contributor
timestamp: September 03, 2019, 10:07:12 am
content: Quote from: natiz on September 02, 2019, 09:18:07 pmConnect an oscilloscope to the communication lines and look at the signal. Given it looks like some kind of bus and an 8052 doesn't have any fancy communication peripherals you might be looking at some kind of bit-banged protocol. To which pins are the communication lines connected?

author: Yansi
author_rank: Super Contributor
timestamp: September 03, 2019, 11:06:52 am
content: Show a detailed picture of the underside of the board, dammit!

author: natiz
author_rank: Newbie
timestamp: September 03, 2019, 05:28:08 pm
content: Quote from: mjs on September 03, 2019, 07:46:54 amI was suspecting that it might be something related to the DSC boards.Following that thread, I found this interface for arduino/esp -https://github.com/taligentx/dscKeybusInterfaceWill give it a try and update

author: Bassman59
author_rank: Super Contributor
timestamp: September 03, 2019, 07:15:36 pm
content: Quote from: natiz on September 02, 2019, 09:18:07 pmIt's a standard 8051, so the only communication port it has is a UART. The documentation for the 8051 UART is readily available.

author: natiz
author_rank: Newbie
timestamp: January 19, 2020, 09:34:09 pm
content: Update:So I tried using a couple of DSC libs below, all gave me unreadable data.https://github.com/sjlouw/dsc-alarm-arduinohttps://github.com/taligentx/dscKeybusInterfacehttps://github.com/dougkpowers/pc1550-interfaceSince I don't have a scope, I hooked up an Arduino Uno to the bus and wrote a simple code that reads the data pin on clock interrupt and counts the number of times and the interval in micros between the clock rising.If found that every 80 bits read (81 actually), the interval between the last clock rising is around ~11ms (more than 10500 microseconds), and that after 19 cycles, there is one cycle of 91 bits.Still trying to make sense ofthe data.

author: Renate
author_rank: Super Contributor
timestamp: January 21, 2020, 02:55:06 pm
content: I don't think that you actually mentioned the clock rate.Are you sampling on the falling or rising edge of the clock?I don't think that it's DSC because the signal levels aren't 12V.

author: Yansi
author_rank: Super Contributor
timestamp: January 21, 2020, 04:51:10 pm
content: Still can't show use the photo of the bottom side of the PCB, so we can make a better guess at what ICs and protocols might be used for interfacing.

author: Renate
author_rank: Super Contributor
timestamp: January 21, 2020, 05:03:03 pm
content: Quote from: Yansi on January 21, 2020, 04:51:10 pmI would guess that there is nothing there, the PCB looks primitive.You've got a single transistor to pull down an OC data line. That's it.