
8/18/97 Am29F800T/Am29F800B 17
PRELIMINARY
cause DQ6 to toggle. See Figure 12 for the Toggle Bit
timing specifications and diagrams.
DQ5: Exceeded Timing Limits
DQ5 will indic ate if the program or era se time has ex-
ceeded the specified limits (internal pulse count).
Under these conditions DQ 5 w ill produce a “1”. This is
a failu re cond ition which indica tes tha t the pro gram o r
erase cycle was not successfully completed. Data Poll-
ing is the only operating function of the device under
this co ndition . The CE circuit will partia lly powe r down
the de vice unde r these conditio ns (to ap proxima tely 2
mA). The OE and WE pins will control the output dis-
able functions as described in Table 1.
The DQ5 failure condition will also appear if a user tries
to program a 1 to a location that is previously pro-
grammed to 0. In this case the device locks out and
never completes the Embedded Program Algorithm.
Hence, the system nev er reads a valid dat a on DQ7 bit
and DQ6 never stops t oggling. Once t he device has e x-
ceeded timing limits, the DQ5 bit will indicate a “1”.
Please note that this is not a device failure condition
since the device was incorrectly used. If this occurs,
reset the dev ice .
DQ3: Sector Erase T imer
After the completion of the initial sector erase com-
mand sequence the sector erase time-out will begin.
DQ3 will remain low until the time-out is complete. Data
Polling and Toggle Bit are valid after the initial sector
erase co mmand sequence.
If Data Polling or the Toggle Bit indicates the device has
been written with a valid eras e command, DQ3 may be
used to determine if the sector erase timer window is
still open. If DQ3 is high (“1”) the internally controlled
erase cycle has begun; attempts to write subsequent
commands (other than Erase Suspend) to the device
will be ignored until the erase operation is completed
as indicat ed by Data Polling or Toggle Bit. If DQ3 is low
(“0”), the device will accept additional sector erase
commands. To insure the command has been ac-
cepted, the system software should check the status of
DQ3 prior to and following each subsequent sector
erase command. If DQ3 were high on the second sta-
tus chec k, the command m ay not have been accept ed.
Refer to Table 8, Hardware Sequence Flags.
DQ2: Toggle Bit 2
This toggle bit, along with DQ6, can be used to deter-
mine whether the device is in the Embedded
Erase Algorith m o r in Erase sus p end.
Successive reads from the erasing sector will cause
DQ2 to toggle during the Embedded Erase Algorithm.
If the device is in the erase suspend-read mode, suc-
cessive reads from the erase-suspend sector will
cause DQ2 to toggle. When the device is in the erase
suspend-program mode, successive reads from the
byte address of t he non- erase s uspend sect or will i ndi-
cate a logic “1” at the DQ2 bit. Not e that a sector whi ch
is selected for erase is not available for read in Erase
Suspend mode. Other sectors which are not selected
for Erase can be read in Erase Suspend.
DQ6 is different from DQ2 in that DQ6 toggles only
when the standard program or erase, or erase sus-
pend-program operation is in progress.
If the DQ5 failure condition is observed while in Sector
Erase mode (i.e., exc eeded timing limits), the DQ2 tog-
gle bit can gi ve extra info rmation. I n thi s case, the nor-
mal fun ction of DQ2 is modified. If DQ5 is at logic “1 ”,
then DQ2 will toggle with consecutive reads only at the
sector address that caused the failure condition. DQ2
will toggle at the sector address where the failure oc-
curred and will not toggle at other sector addresses.
RY/BY: Ready/Busy
The Am29F800 provides a RY/BY open-drain output
pin as a way to indicate to the host system that the Em-
bedded Algorithms are either in progress or have been
comp leted. If the outp ut is low, the devic e is busy with
either a program or erase operation. If the output is
high, the device is ready to accept any read/write or
erase operati on. When the RY/B Y pin is low , th e device
will not accept any additional program or erase com-
mand s with the exc eption of t he Era se Susp end c om-
mand. If the Am 29F800 is plac ed i n an Er ase Sus pend
mode, the RY/BY output will be high.
During programming, the RY/BY pin is driven low afte r
the rising edge of the fourth WE puls e. During an erase
operation, the RY/BY pin is driven low after the rising
edge of the sixth WE pulse . Th e RY/BY pin should be
ignored while RESET is at VIL. Refer to Figure 13 for a
detailed timi ng diagr am.
Since this is an open-drain output, several RY/BY
pins can be tied t ogether in parallel with a pull- up resis-
tor to VCC.
RESET: Hardware Reset
The Am29F800 device may be reset by driving the
RESET pin to VIL. The RESET pin must be kept low
(VIL) for at least 500 ns. Any operation in progress will
be terminated and the internal state machine will be
reset to the read mode 20 µs after the RESET pin is
driven low. Furthermore, once the RESET pin goes
high, the device requires an additional 50 ns before it
will allow read access. When the RESET pin is low, the
device will be in the standby mode for the duration of
the pulse and all the data output pins will be tri-stated.
If a hardware reset occurs during a program or erase
operation, the data at that particular location will
be indeterminate.
The RESET pin may be tied to the system reset input.
Therefore, if a system reset occurs during
the Embedded Program or Erase Algorithm, t he device