AN560 datasheet(11/22 Pages) MICROCHIP

11 / 22 page

DS00560D-page 11

Using the 93LC56 and 93LC66

16c5x/7x Cross-Assembler V4.12 Released

Mon Jun 06 10:49:00 1994

Page 1

Line

Opcode

0001

LIST P=16C54,c=132

0002

;****************************************************************

0003

;

3-Wire Byte Write with Data Poll Program (107 bytes)

0004

;

0005

;

This program demonstrates how to interface a

0006

;

Microchip PIC16C54 to a 93LC56 or 93LC66 Serial EE

0007

;

device. This program will execute the erase/write enable

0008

;

command, write to 8 consecutive addresses, and then

0009

;

use the ‘data polling’ method to determine when the

0010

;

write cycle is complete.

The program then executes

0011

;

the erase/write disable command.

This sequence will

0012

;

repeat forever.

0013

;

0014

;

When writing to a 3-wire serial EE device, the

0015

;

internally timed write cycle will begin after

0016

;

the opcode, address and data are sent to the

0017

;

device.

There are two ways to make sure that the

0018

;

cycle is complete before you send it another command.

0019

;

The simplest method is to simply wait for the maximum

0020

;

write cycle time, which can be obtained from the data book.

0021

;

A more efficient method is “Data polling.”

This is

0022

;

done by toggling the chip select line low and then

0023

;

back high after the opcode, address and data are sent.

0024

;

The chip select line must be low for at least 250ns

0025

;

before bringing it high again.

The device will pull

0026

;

the data out line low at that point, and set it high

0027

;

when the write cycle is complete.

The user can then check

0028

;

or “poll” the dataout line until it goes high before

0029

;

sending the next command.

0030

;

0031

;

As an option, the user can connect a LED to pin 18

0032

;

on the PIC16C54 (use about a 1K resistor in series) as a

0033

;

timeout indicator.

This LED will come on if the

0034

;

data polling is unsuccessful and the device being

0035

;

programmed does not respond.

This can be tested by

0036

;

simply running the program with no part in the socket.

0037

;

0038

;

This program communicates to the serial EE in the

0039

;

x16 mode, and ASSUMES THE USER HAS SET THE ORG PIN

0040

;

ON THE DEVICE TO Vcc.

0041

;

0042

;

Timing is based on using the PIC16C54 in ‘XT’ mode

0043

;

using a 4Mhz crystal.

Clock speeds to the serial EE

0044

;

will be approximately 50 kHz for this setup.

0045

;

0046

;

PIC16C54 to Serial EE Connections:

0047

;

0048

;

PIC16C54

Serial EE

0049

;

——————

0050

;

Pin 10 (RB4) —> Chip Select

0051

;

Pin 11 (RB5) —> Clock

16c5x/7x Cross-Assembler V4.12 Released

Mon Jun 06 10:49:00 1994

Page 2

Line

Opcode

0052

;

Pin 12 (RB6) —> Data In

0053

;

Pin 13 (RB7) —> Data Out

0054

;

ORG=Vcc

0055

;

0056

;************************************************************

0057

;

0058

;************************************************************

0059

0005

port_a

equ

; port 5 (port_a)

0060

0006

port_b

equ

; port 6 (port b) used comm lines to serial EE

8-109

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