M28C64C datasheet(4/15 Pages) STMICROELECTRONICS

4 / 15 page

AI00877C

ADDRESS

LATCH

A5-A12

(Page Address)

ATD & CONTROL LOGIC

64K ARRAY

ADDRESS

LATCH

A0-A4

Y DECODE

VPP GEN

RESET

SENSE AND DATA LATCH

I/O BUFFERS

PAGE LOAD

TIMER STATUS

TOGGLE BIT

DATA POLLING

DQ0-DQ7

Figure 3. Block Diagram

Microcontroller Control Interface

The M28C64C provides two write operation status

bits and one status pin that can be used to minimize

the system write cycle. These signals are available

on the I/O port bits DQ7 or DQ6 of the memory

during programming cycle only, or as the RB signal

on a separate pin.

DQ7

DQ6 DQ5 DQ4 DQ3 DQ2 DQ1 DQ0

PLTS Hi-Z

Hi-Z

Figure 4. Status Bit Assignment

DP = Data Polling

TB = Toggle Bit

PLTS = Page Load Timer Status

Data Polling bit (DQ7). During the internal write

cycle, any attempt to read the last byte written will

produce on DQ7 the complementary value of the

previously latched bit. Once the write cycle is fin-

ished the true logic value appears on DQ7 in the

read cycle.

Toggle bit (DQ6). The M28C64C offers another

way for determining when the internal write cycle

is completed. Duringthe internal Erase/Write cycle,

DQ6 will toggle from ”0” to ”1” and ”1” to ”0” (the

first read value is ”0”) on subsequent attempts to

read any address in the memory. When the internal

cycle is completed the toggling will stop and the

device will be accessible for a new Read or Write

operation.

Page Load Timer Status bit (DQ5). In the Page

Write mode data may be latched by E or W up to

100

µs after the previous byte. Up to 32 bytes may

be input. The Data output (DQ5) indicates the

status of the internal Page Load Timer. DQ5 may

be read by asserting Output Enable Low (tPLTS).

DQ5 Low indicates the timer is running,

High

indicates time-out after which the write cycle will

start and no new data may be input.

Ready/Busy pin. The RB pin provides a signal at

its open drain output which is low during the

erase/write cycle, but which is released at the

completion of the programming cycle.

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