AM28F020 datasheet(15/35 Pages) AMD

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Am28F020

the Erase-verify command (section D). Addresses are

latched on the falling edge of the WE# pulse.

Another software timing routine (6 µs duration) must be

executed to allow for generation of internal voltages for

margin checking and read operation (section E).

During Erase-verification (section F) each address that

returns FFh data is successfully erased. Each address

of the array is sequentially verified in this manner by re-

peating sections D thru F until the entire array is veri-

fied or an address fails to verify. Should an address

location fail to verify to FFh data, erase the device

again. Repeat sections A thru F. Resume verification

(section D) with the failed address.

Each data change sequence allows the device to use

up to 1,000 erase pulses to completely erase. Typically

100 erase pulses are required.

Note: All address locations must be programmed to

00h prior to erase. This equalizes the charge on all

memory cells and ensures reliable erasure.

FLASHRITE PROGRAMMING SEQUENCE

Program Setup

The device is programmed byte by byte. Bytes may be

programmed sequentially or at random. Program Setup

is the first of a two-cycle program command. It stages

the device for byte programming. The Program Setup

operation is performed by writing 40h to the command

Program

Only after the program Setup operation is completed

will the next WE# pulse initiate the active programming

operation. The appropriate address and data for pro-

gramming must be available on the second WE# pulse.

Addresses and data are internally latched on the falling

and rising edge of the WE# pulse respectively. The ris-

ing edge of WE# also begins the programming opera-

tion. You must write the Program-verify command to

terminate the programming operation. This two step

sequence of the Setup and Program commands helps

to ensure that memory contents are not accidentally

written. Also, programming can only occur when high

voltage is applied to the VPP pin and all control pins are

in their proper state. In absence of this high voltage,

memory contents cannot be programmed.

Refer to AC Characteristics and Waveforms for specific

timing parameters.

Program Verify Command

Following each programming operation, the byte just

programmed must be verified.

Write C0h into the command register in order to initiate

the Program-verify operation. The rising edge of this

WE pulse terminates the programming operation. The

Program-verify operation stages the device for verifica-

tion of the last byte programmed. Addresses were pre-

viously latched. No new information is required.

Margin Verify

During the Program-verify operation, the device applies

an internally generated margin voltage to the ad-

dressed byte. A normal microprocessor read cycle out-

puts the data. A successful comparison between the

programmed byte and the true data indicates that the

byte was successfully programmed. The original pro-

grammed data should be stored for comparison. Pro-

gramming then proceeds to the next desired byte

location. Should the byte fail to verify, reprogram (refer

to Program Setup/Program). Figure 3 and Table 5 indi-

cate how instructions are combined with the bus oper-

ations to perform byte programming. Refer to AC

Programming Characteristics and Waveforms for spe-

cific timing parameters.

Flashrite Programming Algorithm

The device Flashrite Programming algorithm employs

an interactive closed loop flow to program data byte by

byte. Bytes may be programmed sequentially or at ran-

dom. The Flashrite Programming algorithm uses 10 µs

programming pulses. Each operation is followed by a

byte verification to determine when the addressed byte

has been successfully programmed. The program al-

gorithm allows for up to 25 programming operations per

byte per reprogramming cycle. Most bytes verify after

the first or second pulse. The entire sequence of pro-

gramming and byte verification is performed with high

voltage applied to the VPP pin. Figure 3 and Table 5 il-

lustrate the programming algorithm.

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