ISA Pin Configuration Chapter 6
Normally, DRQ remains asserted as long as accesses can be made to the FIFOs. You can use the TIMER register and the TMOE and TIM/BYTN bits of the CFG to limit the assertion time of the DRQ signal. In most ISA systems, you should limit the DRQ assertion time.
DRQ is an output-only pin. If the application does not require DMA, you can leave DRQ unconnected.
DACKN
The DACKN signal selects the FIFOs for access. In the ISA pin configuration, the
TNT4882 supports only 16-bit DMA.
If the DMAEN bit in the ACCWR register is clear, the TNT4882 ignores the DACKN pin. See the Accessory Write Register (ACCWR) section in Chapter 3, TNT4882 Interface
Registers.
The DACKN pin is an active low input-only pin with an internal pull-up resistor. If the application does not require DMA, you can connect DACKN to Vdd or leave DACKN unconnected.
INTR
The INTR pin asserts when an enabled interrupt in ISR3 asserts. (See the Hardware
Interrupts section in Chapter 4, TNT4882 Programming Considerations.) The INTR pin can be tristated by clearing the INTEN bit in the INTR register. (See the Board Interrupt
Register section in Chapter 3, TNT4882 Interface Registers.) There is no minimum pulse width for the assertion of the INTR pin.
IOCHRDY
The TNT4882 drives IOCHRDY low to indicate that the current I/O cycle must be lengthened. IOCHRDY unasserts (floats high) during write cycles when the TNT4882 has latched the data from the ISA bus. IOCHRDY unasserts during read cycles when data is valid on the data pins.
The TNT4882 does not drive IOCHRDY low during DMA cycles or when the TNT4882 is in one-chip mode. In Turbo+7210 mode or Turbo+9914 mode, the TNT4882 drives
IOCHRDY low during accesses to registers in 7210 or 9914 space. The TNT4882 considers the following offsets to be in 7210 or 9914 space: 0, 2, 4, 6, 8, A, C, E, 11, 13,
15, 17, 1B, 1D, 1F.
The IOCHRDY pin is driven with an open-collector driver. Normally, an internal pull-up resistor passively pulls this signal to a high logic level.
TNT4882 Programmer Reference 6-4 © National Instruments Corp.
