M672061H
Expansion In (XI)
Full Flag (FF)
This input is a dual-purpose pin. Expansion In (XI) is connected to GND to indicate an
operation in the single device mode. Expansion In (XI) is connected to Expansion Out
(XO) of the previous device in the Depth Expansion or Daisy Chain modes.
The Full Flag (FF) will go low, inhibiting further write operations when the write pointer is
one location less than the read pointer, indicating that the device is full. If the read
pointer is not moved after Reset (RS), the Full Flag (FF) will go low after 16384 writes.
Empty Flag (EF)
The Empty Flag (EF) will go low, inhibiting further read operations when the read pointer
is equal to the write pointer, indicating that the device is empty.
Expansion Out/Half-full
Flag (XO/HF)
This is a dual-purpose output. In the single device mode, when Expansion In (XI) is con-
nected to ground, this output acts as an indication of a half-full memory.
The M672061H offers a variable offset for the Half Full condition. The offset is loaded
into a register during a reset cycle. When RS is low, the Programmable Half Full Flag
(PHF) can be loaded from the DATA inputs I0 - I8 by pulsing W low or from the DATA
outputs Q0 - Q8 by pulsing R low. The offset options are listed in table 1. If PHF is not
loaded during the reset cycle, the default offset will be the half of the total memory of the
device.
The Programmable Half-Full Flag (PHF) will be set to low and will remain set until the
difference between the write and read pointers is less than or equal to the Programma-
ble offset (if the Half Full Flag register has been loaded during the reset cycle) or the half
of the total memory (if the Half Full register has not been loaded during the reset cycle).
After half the memory is filled and on the falling edge of the next write operation, the
Half-Full Flag (HF) will be set to low and will remain set until the difference between the
write and read pointers is less than or equal to half of the total memory of the device.
The Half-Full Flag (HF) is then reset by the rising edge of the read operation.
In the Depth Expansion Mode, Expansion In (XI) is connected to Expansion Out (XO) of
the previous device. This output acts as a signal to the next device in the Daisy Chain by
providing a pulse to the next device when the previous device reaches the last memory
location.
Data Output (Q0 - Q8)
DATA output for 9-bit wide data. This data is in a high impedance condition whenever
Read (R) is in a high state.
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4144K-AERO-04/07
ATMEL [ ATMEL ]
