Help with Servo Board using MC908 Microcontroller - Page 1
Forum section: electronics / beginners

author: JunkYardCNC
author_rank: Newbie
timestamp: March 05, 2018, 04:26:58 pm
content: Hello AllMy name is Alan and I am new to this board and fairly new to electronics in general. I became interested in electronics a few years ago when I became interested in CNC machines and Automation/Robotics in general. My knowledge base is fairly slim but I do a good amount of reading and researching however I do not have a deep grasp on the more rudimentary basics ofcomplexcircuits and low level communication (serial, parallel, etc.) so I really find that I hit a wall any time I run into anything that is written for an actual electrical engineer or programmer like the datasheet for a micro controller. I have some experience with Arduino and Raspberry Pi, but all of it on a very low, basics to make it work, level so no extensive programming or circuit designing as of yet.Now that I have given a little intro with my skill and knowledge level let me get to my reason for posting.As I said I got into electronics because I have an interest in Automation/Robotics/CNC, and as part of my quest, I bought a lot of parts from a guy on Craigslist that turned out to be the internal robotics from a Pharmacy prescription filling machine, like the ones you see in the back of the pharmacy with a computer screen and rows and rows of amber/orangish bins. After spending some time playing around with the stuff and researching all of the part numbers etc. I was able to (obviously) figure out what everything was and how it all basically worked. The guy I bought it from had no idea what he had or what he was doing and was just getting into Electronics Recycling, so he tore apart the Parker Automation Servo Controller(for the two large bldc servos that controlled the two main linear actuators) and the Power Supplies for their e-scrap value!!!!!! Anyway for the smaller motors(some larger brushed with encoders, some small maxon with and with out encoders) there were these small servo boards that seem to be able to run two motors. It is these small servo boards that I am trying to figure out.I have looked up the board numbers etc. and cant find any information specifically on them but being that they are a very specialized part of a larger non-consumer grade machine I wouldn't suspect that much information would be available to anyone outside the company's internal service techs. That being said my next step was to identify all of the microchips and pull the datasheets.Here are all of the chips with all of the markings on them:(1x)MC908SR12CFAE OLO6H CTAA0717 ---- Microcontroller (https://www.mouser.com/ds/2/302/MC68HC908AB32-1126874.pdf)(1x) JM74RDLM629M-6---- Motion Controller Servo/Encoder (http://www.ti.com/lit/ds/symlink/lm629.pdf)(1x) 77F52RKAHCT14---- Hex Inverter Boolean (http://www.ti.com/lit/ds/symlink/sn74ahct14.pdf)(2x)VP30826CM CD07 ---- Low Power RS-485 Transceiver (http://www.ti.com/lit/ds/symlink/sn65hvd3082e.pdf)(2x) JM73ACLMD18200TP+ ---- 3A 55V H-Bridge (http://www.ti.com/lit/ds/symlink/lmd18200.pdf)(1x) ONAN 2675 M5.0 ---- LM2675 Simple Switcher 1A step-down voltage regulator (http://www.ti.com/lit/ds/symlink/lm2675.pdf)Other than the chips there are a bunch of SM components along with 2 power connectors, 2 10 pin connectors, 2 6 pin connectors, 1 10 pin header(this connected to small maxon dc motor with encoder), and one very small side mount 6 pin connector that I am assuming is for programming the board.Now for me the basics of the board are fairly obvious based on the 4 main chips and my basic understanding of motor control, but as soon as I started reading the almost 400pg datasheet for the Microcontroller I realized there was NO WAY I was going to be able to bullshit my way through figuring this thing out!!!!I will try to post a detailed picture of the board but my basic question is as follows:How, does this board work?Can I communicate with the micro-controller on the board and how would I go about doing that?Being that I am new to this I hope I am not asking too much and it is somewhat of a reasonable request. If not please let me know and I will try to revise/simplify my questions to make them more pointed and direct.

author: Benta
author_rank: Super Contributor
timestamp: March 05, 2018, 06:47:41 pm
content: You've got the wrong MCU datasheet.You'll need the datasheet for MC68HC908SR12. The 'AB32 is a different part.

author: JunkYardCNC
author_rank: Newbie
timestamp: March 06, 2018, 02:19:12 am
content: Thanks for catching that!!!Obviously the fact that I didn't even realize shows how lost I am.Could you tell from the actual chip in the pic?