Post by thread:PIC implementation of I2C

I am looking to use I2C on a PIC16C74B. After reading the pages of information in the Data book, I can't seem to tell what's done in hardware and what has to be done by the programmer in software. I know that the ACK is done automatically, but what about the switching of inputs and outputs when a Master is reading instead of transmitting? Do the inputs switch to outputs in hardware or does this have to be done in software? If anyone has a function/subroutine which performs I2C on a PIC, that would be useful in understanding. Any other comments would be appreciated. Thanks, John Bellini

John Bellini wrote: > I am looking to use I2C on a PIC16C74B. After reading the pages of > information in the Data book, I can't seem to tell what's done in > hardware and what has to be done by the programmer in software. > > I know that the ACK is done automatically, but what about the switching > of inputs and outputs when a Master is reading instead of transmitting? > Do the inputs switch to outputs in hardware or does this have to be done > in software? > > If anyone has a function/subroutine which performs I2C on a PIC, that > would be useful in understanding. Any other comments would be > appreciated. You'll end up wasting more time and code space trying to get the built-in I2C to do anything that you can do better in software. I have a few links to good I2C resources at : http://www.wasp.co.za/~tjaart/electronicsearch.html -- Friendly Regards Tjaart van der Walt spam_OUTtjaartTakeThisOuTwasp.co.za |--------------------------------------------------| | WASP International | |R&D Engineer : GSM peripheral services development| |--------------------------------------------------| |SMS .....tjaartKILLspam@spam@sms.wasp.co.za (160 chars max)| | http://www.wasp.co.za/~tjaart/index.html | |Voice: +27-(0)11-622-8686 Fax: +27-(0)11-622-8973| | WGS-84 : 26¡10.52'S 28¡06.19'E | |--------------------------------------------------|

At 10:56 28.07.98 -0700, you wrote: >I am looking to use I2C on a PIC16C74B. After reading the pages of Master or slave mode ? Thomas =8-) -- ********************************************************** * Thomas Magin FON: ++49-761-4543-489 * * marquette-Hellige GmbH FAX: -507 * * E-FW / Emergency Systems email: maginKILLspamhellige.de * * Munzinger Str. 3 * * D-79111 Freiburg / Germany * **********************************************************

In reply to John Bellini's post, Being a master is relatively easy, and done by bit-banging in software. You only need two open-collector outputs for this. In a multimaster environment, the SSP hardware is useful because you can monitor the Start (S) bit to ensure you don't start using the bus if a message has already started. This gives you collision avoidance. Being a slave requires hardware assistance as you don't wish to sit around watching bus signals all the time. The SSP provides this. You set this up to interrupt the CPU every time a complete byte has arrived or departed from the SSP buffer. It is up to your software to handle them. > I know that the ACK is done automatically, > what about the switching of inputs and outputs when > a Master is reading instead of transmitting? > Do the inputs switch to outputs in hardware Yes, the SSP knows the data transf er direction. It only bothers the CPU after the transfer is complete. > If anyone has a function/subroutine which performs I2C on a PIC, > that would be useful in understanding. I can't give you the full source but I can tell you the things that tripped me up and thus you can avoid.

I just wish someone would publish a really good slave implementation. I would publish mine, but it still locks up occasionally, and I think I'd have people swearing at me! My experience has been that too many people have struggled with this bear and have some valuable time invested in these routines, thus are unwilling to share them. Most people, after much struggling, give up and go to a 3 wire bus. Also, the implementation can be so different as you can go multimaster, single master, 400kHz, 100kHz, interrupt, polled.... all of which are specific to the application and require different resources. I've collected many different 'chunks' and hodge podged them together with the SSP interrupts for a bus that runs at 45kHz. Also it's in C. Craig >Being a slave requires hardware assistance as you don't wish to sit >around watching bus signals all the time. The SSP provides this. >You set this up to interrupt the CPU every time a complete byte has >arrived or departed from the SSP buffer. It is up to your software >to handle them. >I can't give you the full source but I can tell you the things >that tripped me up and thus you can avoid.

I put a 16C63 on a board and had no problems. Wrote the code with CCS C Compiler. Look at http://www.emicros.com for the description. Keith Howell wrote: {Quote hidden}> > In reply to John Bellini's post, > Being a master is relatively easy, and done by bit-banging in software. > You only need two open-collector outputs for this. > In a multimaster environment, the SSP hardware is useful because you can > monitor the Start (S) bit to ensure you don't start using the bus > if a message has already started. This gives you collision avoidance. > > Being a slave requires hardware assistance as you don't wish to sit > around watching bus signals all the time. The SSP provides this. > You set this up to interrupt the CPU every time a complete byte has > arrived or departed from the SSP buffer. It is up to your software > to handle them. > > > I know that the ACK is done automatically, > > what about the switching of inputs and outputs when > > a Master is reading instead of transmitting? > > Do the inputs switch to outputs in hardware Yes, the SSP knows the data tran sfer direction. > It only bothers the CPU after the transfer is complete. > > > If anyone has a function/subroutine which performs I2C on a PIC, > > that would be useful in understanding. > > I can't give you the full source but I can tell you the things > that tripped me up and thus you can avoid. -- From: Ron Russ EMICROS - Embedded Micro Software (http://www.emicros.com) CANPORT - Lowest cost PC to Controller Area Network Adapter (http://www.emicros.com/canport.htm) CANTEC11 - 68HC11 SBC with Controller Area Network (http://www.emicros.com/cantec11.htm)

Ron I would be interested to know which CCS library you used. Either the bit bash library or functions written for the on board SPI?? How long have you been useing CCS and how have you found it?? Thanks...Jason {Quote hidden}>I put a 16C63 on a board and had no problems. Wrote the code >with CCS C Compiler. Look at http://www.emicros.com for the >description. > >Keith Howell wrote: >> >> In reply to John Bellini's post, >> Being a master is relatively easy, and done by bit-banging in software. >> You only need two open-collector outputs for this. >> In a multimaster environment, the SSP hardware is useful because you can >> monitor the Start (S) bit to ensure you don't start using the bus >> if a message has already started. This gives you collision avoidance. >> >> Being a slave requires hardware assistance as you don't wish to sit >> around watching bus signals all the time. The SSP provides this. >> You set this up to interrupt the CPU every time a complete byte has >> arrived or departed from the SSP buffer. It is up to your software >> to handle them. >> >> > I know that the ACK is done automatically, >> > what about the switching of inputs and outputs when >> > a Master is reading instead of transmitting? >> > Do the inputs switch to outputs in hardware Yes, the SSP knows the data transfer direction. {Quote hidden}>> It only bothers the CPU after the transfer is complete. >> >> > If anyone has a function/subroutine which performs I2C on a PIC, >> > that would be useful in understanding. >> >> I can't give you the full source but I can tell you the things >> that tripped me up and thus you can avoid. > >-- > >From: Ron Russ > EMICROS - Embedded Micro Software > (http://www.emicros.com) > CANPORT - Lowest cost PC to Controller Area Network Adapter > (http://www.emicros.com/canport.htm) > CANTEC11 - 68HC11 SBC with Controller Area Network > (http://www.emicros.com/cantec11.htm) > >