Page 125 - Making PIC Microcontroller Instruments and Controllers

SOCKE1 UE-|2C SEEFROIII t l 5

Microwire Miuowire is a National Semiconductor standard and is specially suited
to use with their microcontrollers. Though often called a three-wire interface, it is
actually a five-wire interface with four signal lines and a ground.
SPI SPI (serial peripheral interface) oiginated at Molorola. 11 is much like
Miffowire, though the signal names, polarities, and other details vary. Like Microwire,
SPI is oilen rel-e ed to as a three-wire interface, though a read/write intedace actu-
ally requires two data lines, a clock, a chip select, and a common ground, making

Other manufactur€rs Drovide Droducts to meet the standards lhat have be€n established.

Which EEPROM Type Should You Use?

I2C is the best EEPROM type to use ifyou havejust two signal lines 1o spare, or ifyo
have a cabled interface (I2C also has the strongest drivers)-
Ifyou want a clock rate faster than 400 kHz, use Microwire or SPI.
For more on using serial EEPROMS, rcfcr 10 the manulaclure$' pages on the Wcb,
especially the following sites:

I National Semiconduclor
wwwnational.conr,/design/
(Contains many application notes on Microwire)
r Motorola Semiconductor
www.mcu.motsps.com/mc.html
(Onsite microcontroller reterences contain SPI documentation,)

Jan Axelson's article in Circ&t Cclldr is a good source of detailed iDfomation on these
devices. The article can be fbund at wwwlvrcon/files/seeprom.pdf.
The PICBASIC PRO Compiler provides the insnuctions necessary to access these

In dll the programs I have listed in this chapter I have used the programs and docu-
mentation verbatim from the microEngineering Labs Web sitc. I did this fbr two rcasons.
One, to not reinvent the wheel since the work has already been done by microEngineedng
Labs, and two, to expose the readers to how the programs are structured by a pro-
grammer other than myself. Each programmer has his or herown style ofdoing things
and itis well wofth being exposed to the work of other programmers.

Socket U3-I2C SEEPROM

Socket U3 accommodates l2C memory only. Figue 7.2 and Program 7.1 illustratc thc
use of this memory type.