SA25C020 Datasheet, PDF (26/31 Pages) List of Unclassifed Manufacturers – 2Mb EEPROM with 25MHz SPI Bus Interface

Read Electronic Signature
(Read_Id)
The device features an 8-bit Electronic
Signature, whose value for the SA25C020
is 11h. This can be read using the RES
instruction.
The Read Id instruction always provides
access to the Electronic Signature of the
device (except while a Byte/Page Write or
Write Status Register cycle is in progress).
Any Read Id instruction executed while a
Byte/Page Write or Write Status Register
cycle is in progress is not decoded, and
has no effect on the cycle in progress.
The device is first selected by driving CSb
low. The instruction code is followed by
three dummy bytes, each bit being latched
in on SI during the rising edge of SCK.
SA25C020 Advanced Information
SAIFUN
26
The 8-bit Electronic Signature, which
stored in the memory, is then shifted out on
SO, with each bit being shifted out during
the falling edge of SCK. The instruction
sequence is shown in Figure 16.
Driving CSb high after the Electronic
Signature has been read at least once
terminates the Read Id instruction. Sending
additional clock cycles on SCK, while CSb
is driven low causes the Electronic
Signature to be output repeatedly.
When CSb is driven high, the device is put
into Standby mode. The transition to
Standby mode is delayed by t_RES, and CSb
must remain high for at least t_RES(max), as
specified in Table 3 on page 10. Once in
Standby mode, the device waits to be
selected, so that it can receive, decode and
execute instructions.
CS
SCK
SI
SO
0 1 2 3 4 5 6 7 8 9 10 28 29 30 31 32 33 34 35 36 37 38 39
Instruction
High Impedance
3 Dummy
Bytes
23 22 21
MSB
32 1 0
Electonic ID
76543210
MSB
Software Protect Mode
t_RES
Standby Mode
Figure 16. Read Electronic Signature (Read Id) Instruction Sequence