CAT1021, CAT1022, CAT1023
Immediate/Current Address Read
Sequential 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-
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.
¯¯
mation (with the R/W bit set to one), it issues an
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.
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.
Figure 11. Selective Read Timing
S
T
A
R
T
S
T
A
R
T
S
T
O
P
BUS ACTIVITY:
MASTER
SLAVE
ADDRESS
BYTE
ADDRESS (n)
SLAVE
ADDRESS
SDA LINE
S
S
P
A
C
K
A
C
K
A
C
K
N
O
DATA n
A
C
K
Figure 12. Sequential Read Timing
S
T
O
P
BUS ACTIVITY:
MASTER
SLAVE
ADDRESS
DATA n
DATA n+1
DATA n+2
DATA n+x
SDA LINE
P
A
C
K
A
C
K
A
C
K
A
C
K
N
O
A
C
K
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
13
Doc. No. MD-3009 Rev. M
CATALYST [ CATALYST SEMICONDUCTOR ]
