M28F420 datasheet(27/38 Pages) STMICROELECTRONICS

27 / 38 page

Write. Write operations are used to give Instruction

Commands to the memory or to latch input data to

be programmed. A write operation is initiated when

Chip Enable E is Low and Write Enable W is Low

with Output Enable G High. Commands, Input Data

and Addresses are latched on the rising edge of W

or E. As for the Read operation, when BYTE is Low

a byte is input, DQ8-DQ14 are ’don’t care’ and A-1

is an additional address. When BYTE is High a

word is input.

Output Disable. The data outputs are high imped-

ance when the Output Enable G is High with Write

Enable W High.

Standby. The memory is in standby when the Chip

Enable E is High. The power consumption is re-

duced to the standby level and the outputs are high

impedance, independent of the Output Enable G

or Write Enable W inputs.

Power Down. The memory is in Power Down when

RP is low. The power consumption is reduced to

the Power Down level, and Outputs are in high

impedance, independant of the Chip Enable E,

Output Enable G or Write Enable W inputs.

Electronic Signature. Two codes identifying the

manufacturer and the device can be read from

the memories, the manufacturer code for SGS-

THOMSON is 20h, and the device codes are 0F2h

for the M28F410 (Top Boot Block) and 0FAh for the

M28F420 (Bottom Boot Block). These codes allow

programming equipment or applications to auto-

matically match their interface to the characteristics

of the particular manufacturer’s product.

The Electronic Signature is output by a Read Array

operation when the voltage applied to A9 is at VID,

the manufacturer code is output when the Address

input A0 is Low and the device code when this input

is High. Other Address inputs are ignored. The

codes are output on DQ0-DQ7. When the BYTE

signal is High the outputs DQ8-DQ15 output 00h,

when Low these outputs are high impedance and

Address input A-1 is ignored.

The Electronic Signature can also be read, without

raising A9 to VID, after giving the memory the

instruction RSIG (see below).

Instructions and Commands

The memories include a Command Interface (C.I.)

which latches commands written to the memory.

Instructions are made up from one or more com-

mands to perform memory Read, Read Status

gram, Clear Status Register, Erase Suspend and

Erase Resume. These instructions require from 1

to 3 operations, the first of which is always a write

operation and is followed by either a further write

operation to confirm the first command or a read

operation(s) to output data.

A Status Register indicates the P/E.C. status

Ready or Busy, the suspend/in-progress status of

erase operations, the failure/success of erase and

program operations and the low/correct value of

the Program Supply voltage VPP.

The P/E.C. automatically sets bits b3 to b7 and

clears bit b6 & b7. It cannot clear bits b3 to b5. The

(RSR) instruction and cleared by the Clear Status

bits b3 to b7 is shown in Table 7. Bits b0 to b2 are

reserved for future use (and should be masked out

during status checks).

Read (RD) instruction. The Read instruction con-

sists of one write operation giving the command

0FFh. Subsequent read operations will read the

addressed memory array content and output a byte

or word depending on the level of the BYTE input.

Read Status Register (RSR) instruction. The

Read Status Register instruction may be given at

any time, including while the Program/Erase Con-

troller is active. It consists of one write operation

giving the command 70h.SubsequentRead opera-

tions output the contents of the Status Register.

The contents of the status register are latched on

the falling edge of E or G signals, and can be read

until E or G returns to its initial high level. Either E

or G must be toggled to VIH to update the latch.

Additionally, any read attempt during program or

erase operation will automatically output the con-

tents of the Status Register.

Read Electronic Signature (RSIG) instruction.

This instruction uses 3 operations.It consists of one

write operation giving the command 90h followed

by two read operations to output the manufacturer

and device codes. The manufacturer code, 20h, is

output when the address line A0 is Low, and the

device code, 0F2h for the M28F410 or 0FAh for the

M28F420, when A0 is High.

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M28F410, M28F420

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