NS32817

Features:

· Makes DRAM Interface and refresh tasks appear virtually transparent to the CPU, making DRAMs as easy to use as static RAMs
·Specifically designed to eliminate CPU wait states up to 10 MHz or beyond
· Eliminates 15 to 20 SSI/MSI components for significant board real estate reduction, system power savings and the elimination of chip-to-chip AC skewing
· On-board ultra precise delay line
· On-board high capacitive RAS, CAS, WE, and address drivers (specified driving 88 DRAMs directly)
· AC specified for directly addressing up to 8 Megabytes
· Low power/high speed bipolar oxide isolated process
· Upward pin and function compatible with new DP8428/ DP8429 1 Mbit DRAM controller drivers
· Downward pin and function compatible with DP8408A/ DP8409A 64k/256k DRAM controller/drivers
· 4 user selectable modes of operation for Access and Refresh (2 automatic, 2 external)


Application

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.

Specifications

Supply voltage,  V_CC                                   7.0V
Storage Temperature Range      -65 to +150
Input Voltage                                              5.5V
Output Current                                      150 mA
Lead Temp. (Soldering, 10 seconds)          300


Description

The DP8417/8418/8419/8419X represent a family of 256k DRAM Controller/Drivers which are designed to provide "No-Waitstate'' CPU interface to Dynamic RAM arrays of up to 2 Mbytes and larger. Each device offers slight functional variations of the DP8419 design which are tailored for different system requirements. All family members are fabricated using National's new oxide isolated Advanced Low power Schottky (ALS) process and use design techniques which enable them to significantly out-perform all other LSI or discrete alternatives in speed, level of integration, and power consumption.

Each device DP8417/8418/8419/8419X integrates the following critical 256k DRAM controller functions on a single monolithic device: ultra precise delay line; 9-bit refresh counter; fall-through row, column, and bank select input latches; Row/Column address muxing logic; on-board high capacitive-load RAS, CAS, and Write Enable & Address output drivers; and, precise control signal timing for all the above.

There are four device options of the basic DP8419 Controller. The DP8417 is pin and function compatible with the DP8419 except that its outputs are TRI-STATEÉ. The DP8418 changes one pin and is specifically designed to offer an optimum interface to 32 bit microprocessors. The DP8419X is functionally identical to the DP8419, but is available in a 52-pin DIP package which is upward pin compatible with National's new DP8429D 1 Mbit DRAM Controller/ Driver.

Each device DP8417/8418/8419/8419X is available in plastic DIP, Ceramic DIP, and Plastic Chip Carrier (PCC) packaging. In order to specify each device for ``true'' worst case operating conditions, all timing parameters are guaranteed while the chip is driving the capacitive load of 88 DRAMs including trace capacitance. The chip's delay timing logic makes use of a patented new delay line technique which keeps A.C. skew to ±3 ns over the full VCC range of ±10% and temperature range of -55 to +125. The DP8417, DP8418, DP8419, and DP8419X guarantee a maximum RASIN to CASOUT delay of 80 ns or 70 ns even while driving a 2 Mbyte memory array with error correction check bits included. Speed selected options of these devices are shown in the switching characteristics section of this document.

With its four independent RAS outputs and nine multiplexed address outputs, the DP8419 can support up to four banks of 16k, 64k or 256k DRAMs. Two bank select pins, B1 and B0, are decoded to activate one of the RAS signals during an access, leaving the three non-selected banks in the standby mode (less than one tenth of the operating power) with data outputs in TRI-STATE.

The DP8419 has two mode-select pins, allowing for two refresh modes and two access modes. Refresh and access timing may be controlled either externally or automatically. The automatic modes require a minimum of input control signals.

A refresh counter is on-chip and is multiplexed with the row and column inputs. Its contents appear at the address outputs of the DP8419 during any refresh, and are incremented at the completion of the refresh. Row/Column and bank address latches are also on-chip. However, if the address inputs to the DP8419 are valid throughout the duration of the access, these latches may be operated in the fallthrough mode.