Parameter
Symbol
Conditions
Ratings
Unit
min
typ
max
Data setup time
tSU
DI, CL
0.75
s
Data hold time
tHD
DI, CL
0.75
s
Clock low-level time
tCL
CL
0.75
s
Clock high-level time
tCH
CL
0.75
s
CE wait time
tEL
CE, CL
0.75
s
CE setup time
tES
CE, CL
0.75
s
CE hold time
tEH
CE, CL
0.75
s
CE high-level time
tCE
CE
20
ms
Data latch transition time
tLC
1.15
s
Data output time
tDC
DO, CL
0.46
s
tDH
DO, CE
0.46
s
No. 5877-13/14
LC72720N, 72720NM
Differs with the value of
the pull-up resistor used.
DO pin operation
This IC incorporates a RAM data buffer that can hold up to 24 blocks of data. At the point where one block of data is
written to this RAM, the IC issues a read request by switching the DO pin from high to low.
The DO pin always goes high for a fixed period (Tdo = 265 s) after a readout and CE goes low. When all the data in the
data buffer has been read out, the DO pin is held in the high state until a new block of data has been written to the RAM. If
there is data that has not yet been read remaining in the data buffer, the DO pin goes low after the Tdo time has elapsed.
After a synchronization reset, the DO pin is held high until synchronization is established. It goes low at the point where
the IC synchronizes.
1. When the DO pin is high following the 265 s period (Tdo) after data is read out
Here, the buffer is in the empty state, i.e. the state where new data has not been written. After this, when the DO pin
goes low, applications are guaranteed to be able to read out that data without it being overwritten by new data if they
start a readout operation within 480 ms of DO going low.
2. When the DO pin is low following the 265 s period (Tdo) after data is read out
Here, there is data that has not been read out remaining in the data buffer. In this case, applications are guaranteed to
be able to read out that data without it being overwritten by new data if they start a readout operation within 20 ms of
DO going low. (Note that this is the worst case condition.)
Notes: 1. Although an application can determine whether or not there is data remaining in the buffer by checking the DO
level with the above timing, checking the RE and RF flags in the serial data is a preferable method.
2. Applications are not limited to reading out one block of data at a time, but rather can read out multiple blocks
of data continuously as described above. When using this method, if an application references the RE and RF
flags in the data while reading out data, it can determine the amount of data remaining. However, the length of
the period for data readout (the period the CE pin remains high) must be kept under 20 ms.
3. If the DO pin is shared with other ICs that use the CCB interface, the application must identify which IC
issued the readout request. One method is to read out data from the LC72720 and either check whether
meaningful data has been read (if the LC72720 is not requesting a read, data consisting of all zeros will be read
out) or check whether the DO level goes low within the 256 s following the completion of the read (if the DO
pin goes low, then the request was from another IC).
CE pin
DO pin
CE pin
DO pin
(Last data) - 1
Last data
New data
(Last data) - 2
(Last data) - 1
Last data
DO check (Tdo < T)