Porting a GPIB Interface Design Based on the NEC µPD7210 to the TNT4882

This document describes considerations related to porting an IEEE 488 device based on the NEC µPD7210 chip to the TNT4882 chip. The 7210 is a common IEEE 488 interface chip used in many instruments. National Instruments makes the NAT7210, a drop-in replacement for NEC µPD7210. However, in some applications, it may be preferable to port the old hardware and software design to the more powerful TNT4882 IEEE 488 interface chip. The register set of the TNT4882 is a superset of the 7210 register set. As a result, most software written for the 7210 can be used on the TNT4882 with only minor changes.

1. Hardware Considerations
2. Using Interrupts
3. Using DMA

Hardware Considerations

The TNT4882 has several Architecture Modes. Chapter 2 of Reference 1 describes these modes. If you intend to use 7210 code, we recommend that you use the Turbo+7210 architecture mode. If you will be writing mostly new code, we recommend that you use the One Chip architecture mode. We recommend that you use the Generic Pin Configuration of the TNT4882. Refer to Chapter 5 of TNT4882 Programmer's Reference Manual. It is possible to change architecture modes using software. However, you also can choose an architecture mode using hardware. To choose the Turbo+7210 mode, connect the MODE and SWAPN pins to VDD.

Register Map
Once the TNT4882 is in Turbo+7210 mode, use the Register Map shown on page 6 of the TNT4882 Data Sheet. In the top half of the map, use only the columns labeled 7210 Mode. You also can use the register map shown in the TNT4882 Programmer's Reference Manual. Notice that the 7210 registers appear at different offsets than the NEC µPD7210.

Chip Initialization
You need to add one item to the beginning of your chip initialization code--Write the SOFT RESET command (22 hex) to the Command Register (CMDR). This statement resets the Turbo488 circuitry of the TNT4882. After issuing the SOFT RESET command you can configure and use the chip as you would the 7210.

Using Interrupts

7210 interrupts generated by IMR2, IMR1, and IMR0 do not directly drive the TNT4882 interrupt pin; 7210 interrupts assert the internal TLCINT signal. By setting the TLCINT IE bit in IMR3, you can force 7210 interrupts to generate TNT4882 interrupts. See the Hardware Interrupts section in Chapter 4 of the TNT4882 Programmer's Reference Manual.

Using DMA

The 7210 uses DMA to read and write bytes directly to the DIR and DOR registers. The TNT4882 performs DMA accesses to and from the internal FIFOs in Turbo+7210 mode. The 7210 DMA signals (DRRQ, DACK*) cannot be routed to external TNT4882 pins. So, if your design requires DMA accesses to the 7210, you will need to either convert these accesses to programmed I/O or use the TNT4882's FIFOs. See the GPIB Data Transfers section in Chapter 4 of the TNT4882 Programmer's Reference Manual.
Related Links:
TNT4882 Programmer Reference Manual
TNT 4882 Data Sheet

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