82C237 pdf datasheet (CMOS Hig

The 82C237 is a modified version of the 82C37A. The
82C237 is fully software and pin for pin compatible with the
82C37A but provides an additional mode for 16-bit DMA
transfers, as well as enhanced speed. Each channel may be
individually programmed for 8-bit or 16-bit data transfers.
The 82C237 controller can improve system performance by
allowing external devices to transfer data directly to or from
system memory. Memory-to-memory transfer capability is
also provided, along with a memory block initialization feature.
DMA requests may be generated by either hardware or
software, and each channel is independently programmable
with a variety of features for flexible operation.
The 82C237 is designed to be used with an external address
latch, such as the 82C82, to demultiplex the most significant
8 bits of address. An additional latch is required to
temporarily store the most significant 8 bits of data if 16-bit
memory-to-memory transfers are desired. The 82C237 can
be used with industry standard microprocessors such as
80C286, 80286, 80C86, 80C88, 8086, 8088, 8085, Z80,
NSC800, 80186 and others. Multimode programmability
allows the user to select from three basic types of DMA
services, and reconfiguration under program control is
possible even with the clock to the controller stopped. Each
channel has a full 64K address and word count range, and
may be programmed to autoinitialize these registers
following DMA termination (end of process).