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PICs with two USARTs?

 
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edhaslam



Joined: 15 Jul 2005
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PICs with two USARTs?
PostPosted: Mon Nov 14, 2005 7:34 am     Reply with quote
Does anyone know if there are any smaller PICs other than the PIC18F6722 and the PIC18F8722 that have two hardware USARTs?

I'm going to be parsing data from a GPS module and a Honeywell HMR3300 (digital compass module) at 9600 baud, so I'm a little reluctant to use a bit banged method for either. Also, the PCB that I'm laying out is pretty small, so space and tracking is an issue as the aforementioned PICs only come in a TQFP package.

Any advice would be appreciated.

Ed
Ttelmah
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PostPosted: Mon Nov 14, 2005 9:41 am     Reply with quote
The alternative solution, is to use something like the MAX3110, with a smaller PIC. Provided you have SPI, as well as a UART. The 'pity' is that you presumably don't need the RS232 transceivers, since this has the equivalent to a MAX232 'built in', and can buffer both the PIC's port,and it's own port, making it then an efficient use of space. Philips were doing a similar SPI-UART bridge, the SC16IS75x/76x. This is available in much smaller packages, but is relatively 'recent', so availablility may be more of an issue.

Best Wishes
asmallri



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Re: PICs with two USARTs?
PostPosted: Mon Nov 14, 2005 9:52 am     Reply with quote
edhaslam wrote:
Does anyone know if there are any smaller PICs other than the PIC18F6722 and the PIC18F8722 that have two hardware USARTs?

I'm going to be parsing data from a GPS module and a Honeywell HMR3300 (digital compass module) at 9600 baud, so I'm a little reluctant to use a bit banged method for either. Also, the PCB that I'm laying out is pretty small, so space and tracking is an issue as the aforementioned PICs only come in a TQFP package.

Any advice would be appreciated.

Ed


An 18F PIC will have no problem bit banging a 9600 baud modem (assuming you have a fast enough clock). An 18F PIC at 40MHz is capable three serial ports (two bitbanged) at 115Kbps FDX.
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edhaslam



Joined: 15 Jul 2005
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Re: PICs with two USARTs?
PostPosted: Mon Nov 14, 2005 11:21 am     Reply with quote
Ttelmah wrote:
The alternative solution, is to use something like the MAX3110, with a smaller PIC. Provided you have SPI, as well as a UART. The 'pity' is that you presumably don't need the RS232 transceivers, since this has the equivalent to a MAX232 'built in', and can buffer both the PIC's port,and it's own port, making it then an efficient use of space. Philips were doing a similar SPI-UART bridge, the SC16IS75x/76x. This is available in much smaller packages, but is relatively 'recent', so availablility may be more of an issue.

Best Wishes


Yeah, all the signals that I will be parsing will be TTL level, so no need for an RS232 tranceiver. I'll check out the Phillips chip though, is it sounds as though it could be useful.

asmallri wrote:

An 18F PIC will have no problem bit banging a 9600 baud modem (assuming you have a fast enough clock). An 18F PIC at 40MHz is capable three serial ports (two bitbanged) at 115Kbps FDX.


This might have to be the other way of doing it as i'm struggling with the board layout at the moment. Maybe I'll do some tests with a low-end 18Fxxxx device and see how reliable it will be. How do you achieve 40MHz? Is it done by having a 20MHz clock and using the internal PLL?

Many thanks,
Ed
Ttelmah
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PostPosted: Mon Nov 14, 2005 11:25 am     Reply with quote
No, it's done by having a 10MHz clock and the internal PLL.
The PLL, is *4 on most PICs.

Best Wishes
edhaslam



Joined: 15 Jul 2005
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PostPosted: Tue Nov 15, 2005 2:12 am     Reply with quote
Ttelmah wrote:
No, it's done by having a 10MHz clock and the internal PLL.
The PLL, is *4 on most PICs.

Best Wishes


Thanks Ttelmah

Ed
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PostPosted: Tue Nov 15, 2005 5:18 am     Reply with quote
The MAX3100 is also an SPI to UART interface without RS232 buffers.
Check it out.
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