DP8421A Datasheet PDF - National Semiconductor
| Part Number | DP8421A | |
| Description | (DP8420A - DP8422A) microCMOS Programmable 256k/1M/4M Dynamic RAM Controller/Drivers | |
| Manufacturers | National Semiconductor | |
| Logo |  |
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July 1992
DP8420A 21A 22A microCMOS Programmable
256k 1M 4M Dynamic RAM Controller Drivers
General Description
The DP8420A 21A 22A dynamic RAM controllers provide a
low cost single chip interface between dynamic RAM and
all 8- 16- and 32-bit systems The DP8420A 21A 22A gen-
erate all the required access control signal timing for
DRAMs An on-chip refresh request clock is used to auto-
matically refresh the DRAM array Refreshes and accesses
are arbitrated on chip If necessary a WAIT or DTACK out-
put inserts wait states into system access cycles including
burst mode accesses RAS low time during refreshes and
RAS precharge time after refreshes and back to back ac-
cesses are guaranteed through the insertion of wait states
Separate on-chip precharge counters for each RAS output
can be used for memory interleaving to avoid delayed back
to back accesses because of precharge An additional fea-
ture of the DP8422A is two access ports to simplify dual
accessing Arbitration among these ports and refresh is
done on chip
Features
Y On chip high precision delay line to guarantee critical
DRAM access timing parameters
Y microCMOS process for low power
Y High capacitance drivers for RAS CAS WE and DRAM
address on chip
Y On chip support for nibble page and static column
DRAMs
Y Byte enable signals on chip allow byte writing in a word
size up to 32 bits with no external logic
Y Selection of controller speeds 20 MHz and 25 MHz
Y On board Port A Port B (DP8422A only) refresh arbitra-
tion logic
Y Direct interface to all major microprocessors (applica-
tion notes available)
Y 4 RAS and 4 CAS drivers (the RAS and CAS configura-
tion is programmable)
Control
DP8420A
DP8421A
DP8422A
of Pins
(PLCC)
68
68
84
of Address
Outputs
9
10
11
Largest
DRAM
Possible
256 kbit
1 Mbit
4 Mbit
Direct Drive
Memory
Capacity
4 Mbytes
16 Mbytes
64 Mbytes
Access
Ports
Available
Single Access Port
Single Access Port
Dual Access Ports (A and B)
Block Diagram
DP8420A 21A 22A DRAM Controller
TRI-STATE is a registered trademark of National Semiconductor Corporation
Staggered RefreshTM is a trademark of National Semiconductor Corporation
C1995 National Semiconductor Corporation TL F 8588
FIGURE 1
TL F 8588 – 5
RRD-B30M105 Printed in U S A
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2 0 Signal Descriptions
Pin
Name
Device (If not Input
Applicable to All) Output
Description
2 1 ADDRESS R W AND PROGRAMMING SIGNALS
R0 – 10
R0 – 9
DP8422A
DP8420A 21A
I ROW ADDRESS These inputs are used to specify the row address during an access
I to the DRAM They are also used to program the chip when ML is asserted (except
R10)
C0 – 10
C0 – 9
DP8422A
DP8420A 21A
I COLUMN ADDRESS These inputs are used to specify the column address during an
I access to the DRAM They are also used to program the chip when ML is asserted
(except C10)
B0 B1
I BANK SELECT Depending on programming these inputs are used to select a group
of RAS and CAS outputs to assert during an access They are also used to program
the chip when ML is asserted
ECAS0 – 3
I ENABLE CAS These inputs are used to enable a single or group of CAS outputs
when asserted In combination with the B0 B1 and the programming bits these
inputs select which CAS output or CAS outputs will assert during an access The
ECAS signals can also be used to toggle a group of CAS outputs for page nibble
mode accesses They also can be used for byte write operations If ECAS0 is
negated during programming continuing to assert the ECAS0 while negating AREQ
or AREQB during an access will cause the CAS outputs to be extended while the
RAS outputs are negated (the ECASn inputs have no effect during scrubbing
refreshes)
WIN
I WRITE ENABLE IN This input is used to signify a write operation to the DRAM If
ECAS0 is asserted during programming the WE output will follow this input This
input asserted will also cause CAS to delay to the next positive clock edge if address
bit C9 is asserted during programming
COLINC
(EXTNDRF)
I COLUMN INCREMENT When the address latches are used and RFIP is negated
I this input functions as COLINC Asserting this signal causes the column address to
be incremented by one When RFIP is asserted this signal is used to extend the
refresh cycle by any number of periods of CLK until it is negated
ML I MODE LOAD This input signal when low enables the internal programming register
that stores the programming information
2 2 DRAM CONTROL SIGNALS
Q0 – 10
Q0 – 9
Q0 – 8
DP8422A
DP8421A
DP8421A
O DRAM ADDRESS These outputs are the multiplexed output of the R0 – 9 10 and
O C0–9 10 and form the DRAM address bus These outputs contain the refresh
O address whenever RFIP is asserted They contain high capacitive drivers with 20X
series damping resistors
RAS0 – 3
O ROW ADDRESS STROBES These outputs are asserted to latch the row address
contained on the outputs Q0 – 8 9 10 into the DRAM When RFIP is asserted the
RAS outputs are used to latch the refresh row address contained on the Q0 – 8 9 10
outputs in the DRAM These outputs contain high capacitive drivers with 20X series
damping resistors
CAS0 – 3
O COLUMN ADDRESS STROBES These outputs are asserted to latch the column
address contained on the outputs Q0 – 8 9 10 into the DRAM These outputs have
high capacitive drivers with 20X series damping resistors
WE
(RFRQ)
O WRITE ENABLE or REFRESH REQUEST This output asserted specifies a write
O operation to the DRAM When negated this output specifies a read operation to the
DRAM When the DP8420A 21A 22A is programmed in address pipelining mode or
when ECAS0 is negated during programming this output will function as RFRQ
When asserted this pin specifies that 13 ms or 15 ms have passed If DISRFSH is
negated the DP8420A 21A 22A will perform an internal refresh as soon as possible
If DISRFRSH is asserted RFRQ can be used to externally request a refresh through
the input RFSH This output has a high capacitive driver and a 20X series damping
resistor
5
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| Information | Total 58 Pages | |
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