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Forum Index : Microcontroller and PC projects : Serial Through a UART
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| Ray B Senior Member  Joined: 16/02/2007 Location: AustraliaPosts: 219 |
Back in the early IBM PCs a 40 pin 8250 UART (Universal Asynchronous Receiver / Transmit)was used to take over all of the overhead used with serial communications. Amongst the connections needed from a MM would be data lines for D0-7 plus R/W line & maybe a Chip Select line but when data is not being sent to/from the UART the data lines for example could be used for other purposes. Any thoughts on how practical it would it be to use this type of comms controller on one of these external boards that are being developed. Every XT PC onward usually has a 8250 chip on a socket. Comments.... RayB from Perth WA |
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stuarts Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 199 |
I'm sure it would work fine. I've been looking at I2C uarts, but I cant find one I can buy here. Digikey has them, but the shipping cost to Australia is exhorbitant. Stuart Time is nature's way of keeping everything from happening all at once. |
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donmck Guru  Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
That's one of the big problems with ordering from the US. What are the I2C UART prices like Stuart? This may be as you know, our simple answer to practical Maximite serial comms. Cheers Don... https://www.dontronics.com |
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| Ray B Senior Member Joined: 16/02/2007 Location: AustraliaPosts: 219 |
What is the part number of the 12C UARTs. Reality is putting a 30 year old technology bloody big 40 pin IC on a board could be a retrograde effort although it would work but take a lot of data line interfacing to maybe not swallow up to many of the lines available on a MM. RayB from Perth WA |
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| seco61 Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 205 |
Hi All. One other option to use the serial capabilities of the PIC32 chip is to use some of the currently unused pins on the PIC32 (ie pins which have not been connected to anything but have UART capabilities). I have done this with some of my Maximites (see picture), but does involve a bit of delicate soldering. I used wire wrap wire to make the connections. I found a couple of places on the PCB where there were no tracks on top or bottom and drilled some holes to install a couple of extra 4 pin connectors. I then connect the 8 unused pins to these. The unused and unconnected pins are: 4 - U6TX,CN8,RG6 5 - U3RX,CN9,RG7 11 - AN5,CN7,RB5 14 - AN2,CN4,RB2 21 - U5RX,AN8,RB8 33 - RF3 46 - INT0,OC1,RD0 51 - U1TX,RD3 One of the pins is OC1 and hopefully can be used for PWM. It would be nice if a future PCB design would bring all the pins out to connectors. It would also be nice to get a layout supporting the 100 pin chip. Kind regards Gerard Regards Gerard (vk3cg/vk3grs) |
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| stuarts Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 199 |
Don, there are a few. Have a search for 16IS740/750/752/760. Or the MAX3107/3108/3109. I checked out the digikey ad in Silicon Chip and they wanted $39.95 US to ship a single part. James has found one on Ebay around $12 with $5 shipping. I've just found that element14 have the 16is740 for $3.11. Cant go far past that. Stuart Time is nature's way of keeping everything from happening all at once. |
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ksdesigns Senior Member Joined: 25/06/2011 Location: United StatesPosts: 143 |
Im about done with my i2c to serial adapter .. it uses a pic12f1822 about 1.40$ from digikey and you can probably get free samples from microchip its a 8pin chip so 2 for i2c 2 for serial and 2 for onewire if i get around to it will also write some basic code to program it from the maximite ken |
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| donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
I found out it isn't old age that makes you lose your memory, your brain has a limited capacity, just like any memory system. You shovel it in the front, and when it is full, it falls out the back. When I got to 50, it reached capacity, now it acts as a FIFO Buffer. First in, first out. I have intentions of bringing all unused pins to to an additional header in a future version, but to do a 100 pin version seems to be outside the limitations of what MM is all about at the moment, let alone MM-Basic, but that could well change. Gerard, thanks for the additional pin numbers, I'll note them on my blog, else the details may be FIFO'd out. http://www.themaximitecomputer.com/maximite-control/ Stuart thanks for the feed back on the I2C UART. Sounds like a plan. Ken, love your idea. Are these a OTP ( I doubt, but for the benefit of forum readers), flash, boot-load, sorry once upon a time I could rattle off the range of PIC chips, but I lost track. Of course wondering how the average Maxiteer copes with programming a pic chip. Available in DIP also? If DIP, and flash, and Ken writes a programmer driver for the Maximite, then perhaps the user can program their own, and plug it from his programmer board to his apps board. Perhaps this is one board, even if it is different sockets. Prog/Run 
Cheers Don... https://www.dontronics.com |
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| rhamer Senior Member Joined: 06/06/2011 Location: AustraliaPosts: 174 |
Why are you guys rushing to jerry rig something that is already being done by Geoff? He has promised and is delivering serial, so really anything that is being done now is either a waste of time or some sort of left field non-Maximite standard. You just need to be patient and there will be no need to worry about shipping costs or anything else..... Regards Rohan Rohan Hamer HAMFIELD Software & Hardware Solutions Makers of the Maximite Expander. http://www.hamfield.com.au |
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| donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
Hi Rohan, You are quite correct. One often looses sight of the direction you are heading, when your altimeter is giving false readings, and you spend more time worrying about that, than what you should be concentrating on. There is a small group of Forum members wanting to get I2C going. Ken and Stuart are well involved with this. It appears that Ken's recompiled firmware will produce the BASIC commands, that can be added to Geoff's firmware in a modular fashion. They have then both proposed how easy it will be to get from I2C to a simple UART with an addition IC costing a dollar or two. This will allow them to then drive RS-232 and RS-485, as well as the TTL equivalents of course. I know Geoff will look at serial routines possibly when he returns from his travels, but this will be September? In that two months, I'll bet Ken and Stuart will be able to jerry rig what they want to achieve, and this UART conversion could well be lost time for them, and it may not be the ultimate answer for everyone. But they will achieve it, learn a lot, and have fun doing it. Stuart has also told me that there isn't an RX-TX pair in the I/O header, so I'm not sure where this places serial I/O routines. That will be up to Geoff. Cheers Don... https://www.dontronics.com |
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| rhamer Senior Member Joined: 06/06/2011 Location: AustraliaPosts: 174 |
If your just doing it for fun/interest, then fair enough. But, I can assure you that serial comms from Geoff is well underway. And as my old english teacher used to preach "Patience is a virtue" 
Regards Rohan Rohan Hamer HAMFIELD Software & Hardware Solutions Makers of the Maximite Expander. http://www.hamfield.com.au |
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| donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
Strange Rohan, my black-smith teacher used to say, "He who hesitates is lost" 
I'll bet they don't make black-smith teachers today. Cheers Don... https://www.dontronics.com |
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| rhamer Senior Member Joined: 06/06/2011 Location: AustraliaPosts: 174 |
See, I think both those old proverbs still apply. Be patient if relying on someone else. Or Don't hesitate if relying on yourself. Or maybe it was something like "A fool and his money are easily parted".... 
Cheers Rohan Rohan Hamer HAMFIELD Software & Hardware Solutions Makers of the Maximite Expander. http://www.hamfield.com.au |
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| donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
I know how that one works Rohan, as I found out how to make a small fortune on the stock exchange. You start off with a large fortune. 
Cheers Don... https://www.dontronics.com |
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| seco61 Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 205 |
Hi Don. Just a quick update on 2 of the "spare" MCU pins. Pin 4 is also the SCK2 pin and as such is used by the SPI 2 interface. It provides a 20MHz clock signal as the SPI 2 is in "SPI Master Slave Frame" mode and as such has a free running clock signal. The SPI 2 module is used as part of the video generation system. (However, this pin could be useful for an idea that I have...). Pin 5 is also allocated to the SPI 2 module. It is the SDI2 pin (SPI input) and therfore is not available for use. regards Gerard Regards Gerard (vk3cg/vk3grs) |
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| stuarts Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 199 |
Gerard, I am pretty sure that its pin 4 and 5 that Richard has used for the embedded RTC in the Maximite SM1. might be worth avoiding them if possible. Stuart Time is nature's way of keeping everything from happening all at once. |
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| donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
Thanks Gerard, have added to: http://www.themaximitecomputer.com/maximite-control/ Cheers Don... https://www.dontronics.com |
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| donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
Richard's schematic: Schematics and all other relevant files are available from: http://www.themaximitecomputer.com/max/Programs/Hardware/tct ech/ However a much nicer entry to this directory listing is from: http://www.themaximitecomputer.com/max/Programs/ Then Select Hardware, then tctec Cheers Don... https://www.dontronics.com |
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| seco61 Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 205 |
Hi Stuart. I just had a quick look at the schematic for the SM1. I see that Richard is indeed using pins 4 and 5 for his I2C interface (I2C 4) to the PCF8563. To use those pins for I2C, the video "subsystem" would have to be stopped as they are also part of the SPI 2 module. And stopping the video would also stop the USB handling as that is done during the timer 3 interrupt that drives the video vertical sync state engine. I would be interested to see how the communication with the RTC is to be handled. Regards Gerard Regards Gerard (vk3cg/vk3grs) |
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| donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
This is what Geoff was talking about. It is a real muddle on some of the uses of the pins, and what can be clearly defined with MM-Basic. Just had a quick look at the pfc8563. I2C being multi-drop, I'll have a guess and say the RTC address has been specified in silicon, as there appears to be no external hardware addressing method. So you just read-write to a specific set of registers with I2C protocol. Richard or Stuart, will verify that, or tell me that I am off the planet again. People who remain silent never make mistakes.
Cheers Don... https://www.dontronics.com |
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