DEVICE OPERATION
Read
Read operations are initiated b y both OE and CE LO W.
The read operation is terminated by either CE or OE
returning HIGH. This two line control architecture elimi-
nates bus contention in a system environment. The
data bus will be in a high impedance state when either
OE or CE is HIGH.
Write
Write operations are initiated when both CE and WE
are LOW and OE is HIGH. The FT28C512/513 supports
both a CE and WE controlled write cycle. That is, the
address is latched by the falling edge of either CE or
WE, whichever occurs last. Similarly, the data is
latched internally by the rising edge of either CE or
WE, whichever occurs first. A byte write operation,
once initiated, will automatically continue to comple-
tion, typically within 5ms.
Page Write Operation
The page write feature of the FT28C512/513 allows the
entire memor y to be wr itten in 2.5 seconds. Page write
allows tw o to one hundred twenty-eight b ytes of data to
be consecutively written to the FT28C512/513, prior to
the commencement of the internal programming cycle.
The host can fetch data from another device within the
system during a page write operation (change the
source address), but the page address (A
7
through
A
15
) for each subsequent valid write cycle to the part
during this operation must be the same as the initial
page address.
The page write mode can be initiated dur ing any wr ite
operation. Follo wing the initial byte write cycle, the host
can write an additional one to one hundred twenty-
seven bytes in the same manner as the first byte was
written. Each successive byte load cycle, started by
the WE HIGH to LOW transition, must begin within
100µs of the f alling edge of the preceding WE. If a sub-
sequent WE HIGH to LOW transition is not detected
within 100µs, the internal automatic programming
cycle will commence. There is no page write window
limitation. Effectively, the page write window is infinitely
wide, so long as the host continues to access the
de vice within the byte load cycle time of 100µs .
Write Operation Status Bits
The FT28C512/513 provides the user two write opera-
tion status bits. These can be used to optimise a sys-
tem write cycle time. The status bits are mapped onto
the I/O bus as sho wn in Figure 1.
Figure 1. Status Bit Assignment
DATA Polling (I/O
7
)
The FT28C512/513 features DATA polling as a method
to indicate to the host system that the byte write or
page write cycle has completed. DATA Polling allows a
simple bit test operation to determine the status of the
FT28C512/513, eliminating additional interrupt inputs or
external hardware. During the internal programming
cycle, any attempt to read the last byte written will pro-
duce the complement of that data on I/O
7
(i.e. write
data = 0xxx xxxx, read data = 1xxx xxxx). Once the
programming cycle is complete, I/O
7
will reflect true
data.
Toggle Bit (I/O
6
)
The FT28C512/513 also provides another method for
determining when the inter nal write cycle is complete.
During the inter nal programming cycle, I/O
6
will toggle
from HIGH to LOW and LOW to HIGH on subsequent
attempts to read the device. When the internal cycle is
complete, the toggling will cease, and the device will
be accessible f or additional read or write operations .
5TBDP 43210I/O
Reserved
Toggle Bit
DATA Polling
FT28C512/513