Page 123 - Making PIC Microcontroller Instruments and Controllers

clocKs, MEMORY AND SOCKETS

Sockets U3. U4. and U5: For Serial

One-Wire Memory Devices

Most PIC microconfol]ers come with a certain aDount of ofl-chip memory This memory
is enough for most applications oeated for these tiny processo$, but there are times when
more memory is needed to get thejob done. The LAB-XI has nve empty 8-pin sockets.
Three of these (the three on the left) are designed ro allow us to experiment with three
types of single-wire memory ICs. The ICs doll'r need just one wire for fuli control, but
the data does go back and fofth on one wire.

Nole Each metnry socket accepts only one Ope of mennry (levice, and onlf one of
the lcs is allowed to be in place at any one time because the lines are sharett between
the sockets, so haying more than one device plugged in can create conficts.
Depending on the type of memory you want to experiment with, one of the ihree
schematics in Figue 7.1 is applicable.
The interfaces that have be€n developed for the three types of one-wire memory
give you the choices you rced for flexibility in board design and layout, but it also means
that a single intedace and protocol wonl work for everything. The intefaces vary jn
speed, number of signal lines, and in other impoftant details.
Since the memories arc all orc-wjre sedal devices, their memory content can vary
irom 128 bytes to 4 kilobytes or more and still maintain the s-pin interface.
The salient chamcteristics of the three types of memory are as follows:

r I2C SEEPROM I2C SEEPROMS are serial, etectrically erasable and program-
mable, read-only memories. They are best suited for applications needing a modest
amount of inexpensive nonvolatile memory where a lot of VO lines are not avail-
able for memory transfers. Requires four lines for control,