CYD01S18V/CYD02S18V
CYD04S18V/CYD09S18V
Document #: 38-06077 Rev. *C
Page 6 of 26
Counter enable (CNTEN) inputs are provided to stall the
operation of the address input and utilize the internal address
generated by the internal counter for fast, interleaved memory
applications. A port’s burst counter is loaded when the port’s
address strobe (ADS) and CNTEN signals are LOW. When the
port’s CNTEN is asserted and the ADS is deasserted, the
address counter will increment on each LOW to HIGH
transition of that port’s clock signal. This will Read/Write one
word from/into each successive address location until CNTEN
is deasserted. The counter can address the entire memory
array, and will loop back to the start. Counter reset (CNTRST)
is used to reset the unmasked portion of the burst counter to
0s. A counter-mask register is used to control the counter
wrap.
Counter Reset Operation
All unmasked bits of the counter and mirror registers are reset
to “0.” All masked bits remain unchanged. A Mask Reset
followed by a Counter Reset will reset the counter and mirror
registers to 00000, as will master reset (MRST).
Counter Load Operation
The address counter and mirror registers are both loaded with
the address value presented at the address lines.
Counter Increment Operation
Once the address counter register is initially loaded with an
external address, the counter can internally increment the
address value, potentially addressing the entire memory array.
Only the unmasked bits of the counter register are incre-
mented. The corresponding bit in the mask register must be
a “1” for a counter bit to change. The counter register is incre-
mented by 1 if the least significant bit is unmasked, and by 2
if it is masked. If all unmasked bits are “1,” the next increment
will wrap the counter back to the initially loaded value. If an
Increment results in all the unmasked bits of the counter being
“1s,” a counter interrupt flag (CNTINT) is asserted.
The next Increment will return the counter register to its initial
value, which was stored in the mirror register. The counter
address can instead be forced to loop to 00000 by externally
connecting CNTINT to CNTRST.[20] An increment that results
in one or more of the unmasked bits of the counter being “0”
will deassert the counter interrupt flag. The example in
Figure 2 shows the counter mask register loaded with a mask
value of 0003Fh unmasking the first 6 bits with bit “0” as the
LSB and bit “16” as the MSB. The maximum value the mask
register can be loaded with is 3FFFFh. Setting the mask
register to this value allows the counter to access the entire
memory space. The address counter is then loaded with an
initial value of 8h. The base address bits (in this case, the 6th
address through the 16th address) are loaded with an address
value but do not increment once the counter is configured for
increment operation. The counter address will start at address
8h. The counter will increment its internal address value till it
reaches the mask register value of 3Fh. The counter wraps
around the memory block to location 8h at the next count.
CNTINT is issued when the counter reaches its maximum
value.
Counter Hold Operation
The value of all three registers can be constantly maintained
unchanged for an unlimited number of clock cycles. Such
operation is useful in applications where wait states are
needed, or when address is available a few cycles ahead of
data in a shared bus interface.
Notes:
18. “X” = “Don’t Care,” “H” = HIGH, “L” = LOW.
19. Counter operation and mask register operation is independent of chip enables.
20. CNTINT and CNTRST specs are guaranteed by design to operate properly at speed grade operating frequency when tied together.
Table 3. Address Counter and Counter-Mask Register Control Operation (Any Port) [18, 19]
CLK
MRST
CNT/MSK
CNTRST
ADS
CNTEN
Operation
Description
X
L
X
X
X
X
Master Reset
Reset address counter to all 0s and mask
register to all 1s.
H
H
L
X
X
Counter Reset
Reset counter unmasked portion to all 0s.
H
H
H
L
L
Counter Load
Load counter with external address value
presented on address lines.
H
H
H
L
H
Counter Readback Read out counter internal value on address
lines.
H
H
H
H
L
Counter Increment Internally increment address counter value.
H
H
H
H
H
Counter Hold
Constantly hold the address value for
multiple clock cycles.
H
L
L
X
X
Mask Reset
Reset mask register to all 1s.
H
L
H
L
L
Mask Load
Load mask register with value presented on
the address lines.
H
L
H
L
H
Mask Readback
Read out mask register value on address lines.
H
L
H
H
X
Reserved
Operation undefined
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