FM25C160
Rev. 2.1
Aug 2003
Page 5 of 14
Data Transfer
All data transfers to and from the FM25C160 occur
in 8-bit groups. They are synchronized to the clock
signal (SCK) and they transfer most significant bit
(MSB) first. Serial inputs are clocked in on the rising
edge of SCK. Outputs are driven on the falling edge
of SCK.
Command Structure
There are six commands called op-codes that can be
issued by the bus master to the FM25C160. They are
listed in the table below. These op-codes control the
functions performed by the memory. They can be
divided into three categories. First, are commands
that have no subsequent operations. They perform a
single function such as to enable a write operation.
Second are commands followed by one byte, either in
or out. They operate on the status register. Last are
commands for memory transactions followed by
address and one or more bytes of data.
Table 1. Op-code Commands
Name
Description
Op-code value
WREN
Set Write Enable Latch
00000110b
WRDI
Write Disable
00000100b
RDSR
Read Status Register
00000101b
WRSR
Write Status Register
00000001b
READ
Read Memory Data
00000011b
WRITE
Write Memory Data
00000010b
WREN - Set Write Enable Latch
The FM25C160 will power up with writes disabled.
The WREN command must be issued prior to any
write operation. Sending the WREN op-code will
allow the user to issue subsequent op-codes for
write operations. These include writing the status
register and writing the memory.
Sending the WREN op-code 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. A write
to the status register has no effect on the WEL bit.
Completing any write operation will automatically
clear the write-enable latch and prevent further
writes without another WREN command. Figure 5
below
illustrates
the
WREN
command
bus
configuration.
WRDI - Write Disable
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=0. Figure
6 illustrates the WRDI command bus configuration.
Figure 5. WREN Bus Configuration
Figure 6. WRDI Bus Configuration
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