CAT1021 datasheet(13/21 Pages) ONSEMI

13 / 21 page

CAT1021, CAT1022, CAT1023

Doc. No. MD-3009 Rev. P

Characteristics subject to change without notice

Immediate/Current Address Read

The CAT1021/22/23 address counter contains the

address of the last byte accessed, incremented by

one. In other words, if the last READ or WRITE

access was to address N, the READ immediately

following would access data from address N + 1. For

N = E = 255, the counter will wrap around to zero

and continue to clock out valid data.

After the

CAT1021/22/23 receives its slave address infor-

mation (with the R/W

¯¯ bit set to one), it issues an

acknowledge,

then

transmits

the

8-bit

byte

requested. The master device does not send an

acknowledge, but will generate a STOP condition.

Selective/Random Read

Selective/Random READ operations allow the

Master device to select at random any memory

location for a READ operation. The Master device

first performs a ‘dummy’ write operation by sending

the START condition, slave address and byte

addresses of the location it wishes to read. After the

CAT1021/22/23 acknowledges, the Master device

sends the START condition and the slave address

again, this time with the R/W

¯¯ bit set to one. The

CAT1021/22/23 then responds with its acknowledge

and sends the 8-bit byte requested. The master

device does not send an acknowledge but will

generate a STOP condition.

Sequential Read

The Sequential READ operation can be initiated by

either the Immediate Address READ or Selective READ

operations. After the CAT1021/22/23 sends the inital 8-

bit byte requested, the Master will responds with an

acknowledge which tells the device it requires more

data. The CAT1021/22/23 will continue to output an 8-

bit byte for each acknowledge, thus sending the STOP

condition.

The data being transmitted from the CAT1021/22/23 is

sent sequentially with the data from address N followed

by data from address N + 1. The READ operation

address counter increments all of the CAT1021/22/23

address bits so that the entire memory array can be

read during one operation.

Figure 11. Selective Read Timing

Figure 12. Sequential Read Timing

SLAVE

ADDRESS

BUS ACTIVITY:

MASTER

SDA LINE

BYTE

ADDRESS (n)

DATA n

SLAVE

ADDRESS

BUS ACTIVITY:

MASTER

SDA LINE

DATA n+x

DATA n

DATA n+1

DATA n+2

SLAVE

ADDRESS

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