82C37A_06 Datasheet, PDF (10/24 Pages) Intersil Corporation – CMOS High Performance Programmable DMA Controller

82C37A
both be ones. See the following diagram and Figure 4 for
Mode register functions and addresses.
Mode Register
76543210
BIT NUMBER
00 Channel 0 select
01 Channel 1 select
10 Channel 2 select
11 Channel 3 select
XX Readback
00 Verify transfer
01 Write transfer
10 Read transfer
11 Illegal
XX If bits 6 and 7 = 11
0 Autoinitialization disable
1 Autoinitialization enable
0 Address increment select
1 Address decrement select
00 Demand mode select
01 Single mode select
10 Block mode select
11 Cascade mode select
Request Register - The 82C37A can respond to requests
for DMA service which are initiated by software as well as by
a DREQ. Each channel has a request bit associated with it in
the 4-bit Request register. These are non-maskable and
subject to prioritization by the Priority Encoder network.
Each register bit is set or reset separately under software
control. The entire register is cleared by a Reset or Master
Clear instruction. To set or reset a bit, the software loads the
proper form of the data word. See Figure 4 for register
address coding, and the following diagram for Request
register format. A software request for DMA operation can
be made in block or single modes. For memory-to-memory
transfers, the software request for channel 0 should be set.
When reading the Request register, bits 4-7 will always read
as ones, and bits 0-3 will display the request bits of channels
0-3 respectively.
Request Register
76543210
BIT NUMBER
Don’t Care,
Write
Bits 4-7
All Ones,
Read
00 Select Channel 0
01 Select Channel 1
10 Select Channel 2
11 Select Channel 3
0 Reset request bit
1 Set request bit
Mask Register - Each channel has associated with it a mask
bit which can be set to disable an incoming DREQ. Each
mask bit is set when its associated channel produces an EOP
if the channel is not programmed to Autoinitialize. Each bit of
the 4-bit Mask register may also be set or cleared separately
or simultaneously under software control. The entire register
is also set by a Reset or Master clear. This disables all
hardware DMA requests until a Clear Mask Register
instruction allows them to occur. The instruction to separately
set or clear the mask bits is similar in form to that used with
the Request register. Refer to the following diagram and
Figure 4 for details. When reading the Mask register, bits 4-7
will always read as logical ones, and bits 0-3 will display the
mask bits of channels 0-3, respectively. The 4 bits of the Mask
register may be cleared simultaneously by using the Clear
Mask Register command (see software commands section).
Mask Register
76543210
BIT NUMBER
Don’t Care
00 Select Channel 0 mask bit
01 Select Channel 1 mask bit
10 Select Channel 2 mask bit
11 Select Channel 3 mask bit
0 Clear mask bit
1 Set mask bit
All four bits of the Mask register may also be written with a
single command.
76543210
BIT NUMBER
Don’t Care,
Write
All Ones,
Read
0 Clear Channel 0 mask bit
1 Set Channel 0 mask bit
0 Clear Channel 1 mask bit
1 Set Channel 1 mask bit
0 Clear Channel 2 mask bit
1 Set Channel 2 mask bit
0 Clear Channel 3 mask bit
1 Set Channel 3 mask bit
Status Register - The Status register is available to be read
out of the 82C37A by the microprocessor. It contains
information about the status of the devices at this point. This
information includes which channels have reached a terminal
count and which channels have pending DMA requests. Bits
0-3 are set every time a TC is reached by that channel or an
external EOP is applied. These bits are cleared upon RESET,
Master Clear, and on each Status Read. Bits 4-7 are set
whenever their corresponding channel is requesting service,
regardless of the mask bit state. If the mask bits are set,
software can poll the Status register to determine which
channels have DREQs, and selectively clear a mask bit, thus
allowing user defined service priority. Status bits 4-7 are
updated while the clock is high, and latched on the falling
10
FN2967.2
March 20, 2006