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TOPIC: Preferred PIC18F USB Chip?

Re: Preferred PIC18F USB Chip? 5 years 9 months ago #16575

  • Jon Chandler
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I'm considering a new version of the TAP-28 board that has a USB PIC18F on it.

My goal is to kept the same form factor as the TAP-28 with the same connector locations and same features (4 LEDs, 2 switches) on the board to the largest extent possible. I'd like any add-on boards that work with the TAP-28 to work with the new board too. An example of this is my AS1106 7-segment LED display board, which is designed to stack with the TAP-28 and connect to the I2C/SPI connector. The PIC18F USB chips loose 3 port pins to D+, Dā€“ and the filter cap needed for Vusb, which requires some sacrifice and changes to the original TAP-28 design.



I'm considering the 18F2550 for the micro but I'm wondering if there's any better choice. As I use Swordfish Basic, I want whichever chip I use to work well with Swordfish. I think Jerry's USB module supports most of the USB parts well now. I also want to stick to a 5v part ā€“ too many things I'm interfacing to are 5 volt parts and the interfacing to a 3.3v micro gets messy.

Any suggestions for a part other than the 18F2550? Mapping of the peripherals seems to vary between the USB chips so I have to plan accordingly.
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Re: Preferred PIC18F USB Chip? 5 years 9 months ago #13596

  • Jon Chandler
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Any comments on the PIC18F25K50? It looks like a decent choice.

Re: Preferred PIC18F USB Chip? 5 years 9 months ago #13597

  • lespic
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Hi, I have no USB experience or for that matter any PIC18 or SF ( what am i doing hitting reply) but yes, do agree about 5v difficulties, My favored current recipe is PIC24FV32KA302 (no USB) Pickit3 with CX16 - MPLABX (currently revisiting old projects on PIC16F asm )Like the look of the TAP28, What about a TAP28 for PIC24 with an FTDI chip....

Les.

Re: Preferred PIC18F USB Chip? 5 years 9 months ago #13598

  • jmessina
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For the 18F and USB, if you want to stick with a 28-pin 5V part then it seems like the 25K50 probably isn't a bad choice. It has less errata (so far), and it's cheaper than the 2550. You get a few more features, but basically they're pretty similar.

If you want anything really different feature-wise then you need to switch over to the 3V 18FJ series.
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Re: Preferred PIC18F USB Chip? 5 years 9 months ago #13599

  • Baldor
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As I understand (I'm not sure 100%), the k parts are updated versions of the non k parts.

All the non LF parts works with 5V.

The main diferences I find betwen 18F2550 and 18F25k50 are:

  • 25k50: "Internal 48MHz Oscillator with USB Accuracy -Via Active Clock Tuning from USB Host". Is not mentioned in the 2550
  • 2550: Capture/Compare/PWM Peripherals:2 CCP
  • 25k50: Capture/Compare/PWM Peripherals:1 ECCP
  • 2550: Timers 1 x 8-bit, 3 x 16-bit
  • 25k50: Timers 2 x 8-bit, 2 x 16-bit
  • 2550: ADC 10 ch, 10-bit
  • 25k50: ADC 14 ch, 10-bit.
Looking at the datashet could bring some more diferences, but these are the main ones.

Also, volume princing is much cheaper for the 18F25K50 than for the 18F2550.
Aprendiz de mucho, maestro de casi nada.
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Re: Preferred PIC18F USB Chip? 5 years 9 months ago #13602

  • Jon Chandler
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Like the look of the TAP28, What about a TAP28 for PIC24 with an FTDI chip....

Les.

Since Swordfish is the language I use, a PIC24 is off the table for now. I should get busy and dig into Firewing but a quick look left me a bit dazed and confused. Despite all of David's efforts, it doesn't appear to be catching on ā€“ most of the posts on the Firewing forum page are from Swordfish users.


I do like a few of the added features on the 'k version, including a DAC output (even if it is only 5 bits) and the FVR (fixed voltage reference) with three voltage options.

It also has a CTMU (charge time measurement unit) to support CapSense (I.e., touch) applications. A CapSense module for Swordfish would be an awesome addition!

Mapping of the peripheral pins on the 'k version seems a little cleaner than on the 18F2550. For instance, on the '2550, the SPI SDO line is shared with the UART RxD line but things are moved around to avoid this on the 'k version. I think I can maintain the function layout of the TAP-28 although the mapping of the switches and LEDs will change a bit.

Thanks for the input everyone.
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