CY7C0850V/CY7C0851V
CY7C0852V/CY7C0853V
Document #: 38-06070 Rev. *D
Page 9 of 29
Counter Interrupt
The counter interrupt (CNTINT) is asserted LOW when an
increment operation results in the unmasked portion of the
counter register being all “1s.” It is deasserted HIGH when an
Increment operation results in any other value. It is also
de-asserted by Counter Reset, Counter Load, Mask Reset
and Mask Load operations, and by MRST.
Retransmit
Retransmit is a feature that allows the Read of a block of
memory more than once without the need to reload the initial
address. This eliminates the need for external logic to store
and route data. It also reduces the complexity of the system
design and saves board space. An internal “mirror register” is
used to store the initially loaded address counter value. When
the counter unmasked portion reaches its maximum value set
by the mask register, it wraps back to the initial value stored in
this “mirror register.” If the counter is continuously configured
in increment mode, it increments again to its maximum value
and wraps back to the value initially stored into the “mirror
register.” Thus, the repeated access of the same data is
allowed without the need for any external logic.
Mask Reset Operation
The mask register is reset to all “1s,” which unmasks every bit
of the counter. Master reset (MRST) also resets the mask
register to all “1s.”
Mask Load Operation
The mask register is loaded with the address value presented
at the address lines. Not all values permit correct increment
operations. Permitted values are of the form 2n – 1 or 2n – 2.
From the most significant bit to the least significant bit,
permitted values have zero or more “0s,” one or more “1s,” or
one “0.” Thus 1FFFF, 003FE, and 00001 are permitted values,
but 1F0FF, 003FC, and 00000 are not.
Mask Readback Operation
The internal value of the mask register can be read out on the
address lines. Readback is pipelined; the address will be valid
tCM2 after the next rising edge of the port’s clock. If mask
readback occurs while the port is enabled (CE0 LOW and CE1
HIGH), the data lines (DQs) will be three-stated. Figure 1
shows a block diagram of the operation.
Counting by Two
When the least significant bit of the mask register is “0,” the
counter increments by two. This may be used to connect the
CY7C0850V/CY7C0851V/CY7C0852V as a 72-bit single port
SRAM in which the counter of one port counts even addresses
and the counter of the other port counts odd addresses. This
even-odd address scheme stores one half of the 72-bit data in
even memory locations, and the other half in odd memory
locations.
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