National Instruments DP8400 User Manual
Page 2
Indicates that there is a 3
kX
pull-up
resistor
on
these outputs when they
are disabled
TL F 5012 – 1
FIGURE 1 DP8409A Block Diagram
TABLE II DP8409A Mode Select Options
Mode
(RFSH)
M1
M0
Mode of Operation
Conditions
M2
0
0
0
0
Externally Controlled Refresh
RF I O e EOC
1
0
0
1
Auto Refresh
Forced
RF I O e Refresh Request (RFRQ)
2
0
1
0
Internal Auto Burst Refresh
RF I O e EOC
3a
0
1
1
All RAS Auto Write
RF I O e EOC
3b
0
1
1
Externally Controlled All RAS Access
All RAS Active
4
1
0
0
Externally Controlled Access
5
1
0
1
Auto Access Slow t
RAH
Hidden Refresh
6
1
1
0
Auto Access Fast t
RAH
7
1
1
1
Set End of Count
Modes 0 3b and 4 provide full control of access and re-
fresh for systems with external memory controllers or for
special purpose applications Here all timing can be directly
controlled by the external system as shown in
Figure 2
Modes 1 5 and 6 provide on-chip automatic access se-
quencing with hidden refresh capability A graphic example
of the automatic access modes of the DP8409A is shown in
Figure 3
All DRAM access timing and control is generated
from one input strobe RASIN no external clock is required
On-chip delays insure proper address and control sequenc-
ing once the valid parallel address is presented to the fall-
through input latches of the DP8409A When the RASIN
transitions high-to-low the decoded RAS output transitions
low strobing the row address into the DRAM array An on-
chip delay automatically generates a guaranteed selectable
(mode 5 or 6) row address hold time At this point the
DP8409A switches the address outputs from the row latch
to the column latch Then another on-chip delay generates
a guaranteed column address set-up time before CAS so
that the CAS output automatically strobes the column ad-
dress into the DRAM array Read or write cycles are con-
trolled by the system through independent control of the WE
buffer that is provided on-chip to minimize delay skewing
The automatic access mode makes the dynamic RAM ap-
pear static with respect to access timing In this mode only
one signal RASIN is needed after valid parallel addresses
are presented to the DP8409A to initiate proper access se-
quencing Access timing (RASIN to CAS) with full output
loading of 88 DRAMs in the auto access mode is deter-
mined by the dash number given on the DP8409A data
sheet All performance characteristics are specified over the
full operating temperature and supply ranges
2