DP8419, DP8419D-70, DP8419N Selling Leads, Datasheet
MFG:NSC Package Cooled:NS D/C:06+
DP8419, DP8419D-70, DP8419N Datasheet download

Part Number: DP8419
MFG: NSC
Package Cooled: NS
D/C: 06+
MFG:NSC Package Cooled:NS D/C:06+
DP8419, DP8419D-70, DP8419N Datasheet download

MFG: NSC
Package Cooled: NS
D/C: 06+
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Datasheet: DP8419D-70
File Size: 537809 KB
Manufacturer: NSC [National Semiconductor]
Download : Click here to Download
PDF/DataSheet Download
Datasheet: DP8419D-70
File Size: 537809 KB
Manufacturer: NSC [National Semiconductor]
Download : Click here to Download
PDF/DataSheet Download
Datasheet: DP8419N-70
File Size: 537809 KB
Manufacturer: NSC [National Semiconductor]
Download : Click here to Download
If one desires a memory interface containing the DP8419 that minimizes the number of external components required, modes 5 and 1 should be used. These two modes provide:
1) Automatic access to memory (in mode 5 only one signal, RASIN, is required in order to access memory)
2) Hidden refresh capability (refreshes are performed automatically while in mode 5 when non-local accesses are taking place, as determined by CS)
3) Refresh request capability (if no hidden refresh took place while RFCK was high, a refresh request is generated at the RFI/O pin when RFCK goes high)
4) Automatic forced refresh (If a refresh request is generated while in mode 5, as described above, external logic should switch the DP8419 into mode 1 to do an automatic forced refresh. No other external control signals need be issued. WAIT states can be inserted into the processor machine cycles if the system tries to access memory while the DP8419 is in mode 1 doing a forced refresh). Some items to be considered when integrating the DP8419 into a system design are:
1) The system designer should ensure that a DRAM access not be in progress when a refresh mode is entered. Similarly, one should not attempt to start an access while a refresh is in progress. The parameter tRFHRL specifies the minimum time from RFSH high to RASIN going low to initiate an access.
2) One should always guarantee that the DP8419 is enabled for access prior to initiating the access (see tCSRL1).
3) One should bring RASIN low even during non-local access cycles when in mode 5 in order to maximize the chance of a hidden refresh occurring.
4) At lower frequencies (under 10 Mhz), it becomes increasingly important to differentiate between READ and WRITE cycles. RASIN generation during READ cycles can take place as soon as one knows that a processor READ access cycle has started. WRITE cycles, on the other hand, cannot start until one knows that the data to be written at the DRAM inputs will be valid a setup time before CAS (column address strobe) goes true at the DRAM inputs. Therefore, in general, READ cycles can be initiated earlier than WRITE cycles.
5) Many times it is possible to only add WAIT states during READ cycles and have no WAIT states during WRITE cycles. This is because it generally takes less time to write data into memory than to read data from memory.
The DP84XX2 family of inexpensive preprogrammed medium Programmable Array Logic devices (PALs) have been developed to provide an easy interface between various microprocessors and the DP84XX family of DRAM controller/ drivers. These PALs interface to all the necessary control signals of the particular processor and the DP8419. The PAL controls the operation of the DP8419 in modes 5 and 1, while meeting all the critical timing considerations discussed above. The refresh clock, RFCK, may be divided down from the processor clock using an IC counter such as the DM74LS393 or the DP84300 programmable refresh timer. The DP84300 can provide RFCK periods ranging from 15.4 ms to 15.6 ms based on an input clock of 2 to 10 MHz. Figure 8 shows a general block diagram for a system using the DP8419 in modes 1 and 5. Figure 9 shows possible timing diagrams for such a system (using WAIT to prohibit access when refreshing). Although the DP84XX2 PALs are offered as standard peripheral devices for the DP84XX DRAM controller/drivers, the programming equations for these devices are provided so the user may make minor modification, for unique system requirements.

