a8237 Programmable DMA Controller Data Sheet
Table 1. a8237 Ports (Part 2 of 2)
Name
niowout
nmemr
nmemw
aout[7..0]
dack[3..0]
dbout[7..0]
Type
Output
Output
Output
Output
Output
Output
Polarity
Low
Low
Low
–
–
–
Description
I/O write output. Write strobe to I/O devices as DMA reads from memory.
Memory read. Read strobe to memory elements during DMA reads or
memory-to-memory transfers.
Memory write. Write strobe to memory elements during DMA writes or
memory-to-memory transfers.
Address output. During DMA service,
aout[7..0]
comprises the least
significant byte of the DMA address.
DMA acknowledge bus. Programmable polarity. Indicates a DMA cycle
has been granted to the peripheral.
Data bus output. The microprocessor reads data from internal registers
via the
dbout[7..0]
bus. Also used to output the most significant byte
of the DMA address and temporary data held during memory-to-memory
transfers.
Altera Corporation
7
ALTERA [ ALTERA CORPORATION ]
