CY15B016Q
The two SPI modes are shown in Figure 4 and Figure 5. The
status of the clock when the bus master is not transferring data is:
WREN - Set Write Enable Latch
The CY15B016Q will power up with writes disabled. The WREN
command must be issued before any write operation. Sending
the WREN opcode allows the user to issue subsequent opcodes
for write operations. These include writing the Status Register
(WRSR) and writing the memory (WRITE).
■ SCK remains at 0 for Mode 0
■ SCK remains at 1 for Mode 3
The device detects the SPI mode from the status of the SCK pin
when the device is selected by bringing the CS pin LOW. If the
SCK pin is LOW when the device is selected, SPI Mode 0 is
assumed and if the SCK pin is HIGH, it works in SPI Mode 3.
Sending the WREN opcode causes the internal Write Enable
Latch to be set. A flag bit in the Status Register, called WEL,
indicates the state of the latch. WEL = ‘1’ indicates that writes are
permitted. Attempting to write the WEL bit in the Status Register
has no effect on the state of this bit – only the WREN opcode can
set this bit. The WEL bit will be automatically cleared on the rising
edge of CS following a WRDI, a WRSR, or a WRITE operation.
This prevents further writes to the Status Register or the F-RAM
array without another WREN command. Figure 6 illustrates the
WREN command bus configuration.
Figure 4. SPI Mode 0
CS
0
1
2
3
4
5
6
7
SCK
SI
Figure 6. WREN Bus Configuration
7
6
5
4
3
2
1
0
MSB
LSB
CS
0
1
2
3
4
5
6
7
SCK
SI
Figure 5. SPI Mode 3
0
0
0
0
0
1
1
0
CS
0
1
2
3
4
5
6
7
HI-Z
SO
SCK
WRDI - Reset Write Enable Latch
The WRDI command disables all write activity by clearing the
Write Enable Latch. The user can verify that writes are disabled
by reading the WEL bit in the Status Register and verifying that
WEL is equal to ‘0’. Figure 7 illustrates the WRDI command bus
configuration.
SI
7
6
5
4
3
2
1
0
MSB
LSB
Power Up to First Access
The CY15B016Q is not accessible for a tPU time after power up.
Users must comply with the timing parameter tPU, which is the
minimum time from VDD (min) to the first CS LOW.
Figure 7. WRDI Bus Configuration
CS
Command Structure
0
1
2
3
4
5
6
7
There are six commands, called opcodes, that can be issued by
the bus master to the CY15B016Q. They are listed in Table 1.
These opcodes control the functions performed by the memory.
SCK
SI
0
0
0
0
0
0
1
0
Table 1. Opcode commands
Name
WREN
Description
Set write enable latch
Write disable
Opcode
0000 0110b
0000 0100b
0000 0101b
0000 0001b
0000 0011b
0000 0010b
HI-Z
SO
WRDI
RDSR
WRSR
READ
WRITE
Read Status Register
Write Status Register
Read memory data
Write memory data
Document Number: 002-10555 Rev. *C
Page 6 of 20