Overview of the Major PIC's

Here I am going to list the major chips that could be considered for making a tag gun. I have not listed all of them. Most importantly, I have not listed chips with 1kx14 or less of code space, or those without A/D converters (except for the PIC16F628A, which is included for comaparison). Also, I have not listed those chips that have been clearly replaced by an "A" version. Chips denoted with a "*" are ones that are possibly going to be in limited supply. I make no claims as to the accuracy of these tables as I have probably made mistakes in their typing. However, I hope that someone else finds this information useful. The A/D converters can be useful for putting several switches on one input. The EEPROM is useful for storing permanate configuration settings, while the USART helps in communicating with other electronic devices. Pulse Width Modulators are very helpful in freeing up the PIC's resources while generating waveforms, which are the basis for tag equipment. With them, it is possible to generate the entire waveform and have the PIC be occupied with other tasks while this is being done.

18 Pin Chips

Chip	Code Size	Ram	EEPROM	PWM	Serial I/O	Comparitors	Internal RC	A/D Channels	Price at Digikey.com
16F716	2k	128	None	1	None	None	None	4x8 bit	2.58
16F628A	2k	224	128	1	AUSART	2	4Mhz internal	0	3.05
16F819	2k	256	256	1	I²C/SPI	None	Internal osc.	5x10 bit	3.70
16F88	4k	368	256	1	AUSART, I²C/SPI	2	Internal osc.	7x10 bit	4.58

The only one of these chips that I have used is the 16F628A. However, from the prices, it appears that the 16F819 might be a better choice. I would consider the 16F716 for a high pin count, low cost chip with A/D converters. Obviously, if cost is not of concern, the 16F88 would appear to be the obvious choice for an 18 pin chip, though programmer support can be a little hard to come by.

28 Pin Chips

Chip	Code Size	Ram	EEPROM	PWM	Serial I/O	Comparitors	Internal RC	A/D Channels	Price at Digikey.com
16F72	2k	128	None	1	I²C/SPI	None	None	5x8 bit	3.45
16F870	2k	128	64	1	AUSART	None	None	5x10 bit	4.63
16F872	2k	128	64	1	MI²C/SPI	None	None	5x10 bit	4.63
16F73	4k	192	None	2	USART, I²C/SPI	None	None	5x8 bit	5.38
16F737*	4k	368	None	3	USART, I²C/SPI	2	8 Mhz	5x10 bit	5.95
16F873A	4k	192	128	2	AUSART, MI²C/SPI	2	None	5x10 bit	6.55
16F76	8k	368	None	2	USART, I²C/SPI	None	None	5x8 bit	6.75
16F767*	8k	368	None	3	USART, I²C/SPI	2	8 Mhz	11x10 bit	6.93
16F876A	8k	368	256	2	AUSART, MI²C/SPI	2	None	5x10 bit	7.05

I have not used any of these chips. From looking at their specs, though, I think that the most obvious choices would be the 16F72 for a low cost, high pin count chip, the 16F870 or 16F872 for a low end, general purpose chip (due to the EEPROM), and the 16F876A for a high end chip. I would probably pass over the 16F873A because it is not that much less expensive than the 16F876A ($0.60 less), and the 16F876A is considerably more spacious.

40 Pin Chips

Chip	Code Size	Ram	EEPROM	PWM	Serial I/O	Comparitors	Internal RC	A/D Channels	Price at Digikey.com
16F871	2k	128	64	1	AUSART	None	None	8x10 bit	5.48
16F74	4k	192	None	2	USART, I²C/SPI	None	None	8x8 bit	6.75
16F747*	4k	368	None	3	USART, I²C/SPI	2	8Mhz	14x10 bit	6.85
16F874A	4k	192	128	2	AUSART, MI²C/SPI	2	None	8x10 bit	7.15
16F77	8k	368	None	2	USART, I²C/SPI	None	None	8x8 bit	7.45
16F777*	8k	368	None	3	USART, I²C/SPI	2	8Mhz	14x10 bit	7.60
16F877A	8k	368	256	2	AUSART, MI²C/SPI	2	None	8x10 bit	7.70

Here, I would go either for the inexpensive 16F871 or the 16F877A. Not much in between appeals to me, partly due to the minimal price difference between the 16F877A and the other chips, and also because the other similarly priced chips do not have EEPROM.

Overview of the Major PIC's

18 Pin Chips

28 Pin Chips

40 Pin Chips

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