M28C16B, M28C17B

6/17

Note: 1. Sampled only, not 100% tested.

Symbol

Parameter

Test Condition

Min.

Max.

Unit

Chip Enable Low to Write Enable Low

1

µs

Write Enable High to Chip Enable High

0

ns

Write Enable Low to Write Enable High

10

ms

Output Enable Low to Write Enable High

1µs

Write Enable High to Write Enable Low

3

ms

Figure 7. Chip Erase AC Waveforms

AI01484B

E

G

W

tWLWH2

tELWL

tGLWH

tWHRH

tWHEH

When SDP is enabled, the memory array can still

have data written to it, but the sequence is more

complex (and hence better protected from inad-

vertent use). The sequence is as shown in Figure

4. This consists of an unlock key, to enable the

write action, at the end of which the SDP continues

to be enabled. This allows the SDP to be enabled,

and data to be written, within a single Write cycle

Software Chip Erase

The contents of the entire memory are erased (set

to FFh) by holding Chip Enable (E) low, and hold-

cleared when a 10 ms low pulse is applied to the

Write Enable (W) signal (see Figure 7 and Table 5

for details).

Status Bits

The devices provide three status bits (DQ7, DQ6

and DQ5), for use during write operations. These

allow the application to use the write time latency

of the device for getting on with other work. These

signals are available on the I/O port bits DQ7, DQ6

and DQ5 (but only during programming cycle,

once a byte or more has been latched into the

memory).

Data Polling bit (DQ7). The internally timed write

has elapsed since the previous byte was latched in

to the memory. The value of the DQ7 bit of this last

byte, is used as a signal throughout this write op-

eration: it is inverted while the internal write oper-

ation is underway, and is inverted back to its

original value once the operation is complete.

Toggle bit (DQ6). The device offers another way

for determining when the internal write cycle is

completed. During the internal Erase/Write cycle,

DQ6 toggles from ’0’ to ’1’ and ’1’ to ’0’ (the first

read value being ’0’) on subsequent attempts to

read any byte of the memory. When the internal

write cycle is complete, the toggling is stopped,

and the values read on DQ7-DQ0 are those of the

addressed memory byte. This indicates that the

device is again available for new Read and Write

operations.

Page Load Timer Status bit (DQ5). An internal

timer is used to measure the period between suc-