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Número de pieza | CS82C37A | |
Descripción | CMOS High Performance Programmable DMA Controller | |
Fabricantes | Harris Corporation | |
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SEMICONDUCTOR
82C37A
March 1997
CMOS High Performance
Programmable DMA Controller
Features
Description
• Compatible with the NMOS 8237A
• Four Independent Maskable Channels with Autoinitial-
ization Capability
• Cascadable to any Number of Channels
• High Speed Data Transfers:
- Up to 4MBytes/sec with 8MHz Clock
- Up to 6.25MBytes/sec with 12.5MHz Clock
• Memory-to-Memory Transfers
• Static CMOS Design Permits Low Power Operation
- ICCSB = 10µA Maximum
- ICCOP = 2mA/MHz Maximum
• Fully TTL/CMOS Compatible
• Internal Registers may be Read from Software
The 82C37A is an enhanced version of the industry standard
8237A Direct Memory Access (DMA) controller, fabricated
using Harris’ advanced 2 micron CMOS process. Pin
compatible with NMOS designs, the 82C37A offers
increased functionality, improved performance, and
dramatically reduced power consumption. The fully static
design permits gated clock operation for even further
reduction of power.
The 82C37A 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 fea-
ture. 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 82C37A is designed to be used with an external
address latch, such as the 82C82, to demultiplex the most
significant 8-bits of address. The 82C37A 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).
Ordering Information
5MHz
CP82C37A-5
IP82C37A-5
CS82C37A-5
IS82C37A-5
CD82C37A-5
ID82C37A-5
MD82C37A-5/B
5962-9054301MQA
MR82C37A-5/B
5962-9054301MXA
PART NUMBER
8MHz
CP82C37A
IP82C37A
CS82C37A
IS82C37A
CD82C37A
ID82C37A
MD82C37A/B
5962-9054302MQA
MR82C37A/B
5962-9054302MXA
12.5MHz
CP82C37A-12
IP82C37A-12
CS82C37A-12
IS82C37A-12
CD82C37A-12
ID82C37A-12
MD82C37A-12/B
5962-9054303MQA
MR82C37A-12/B
5962-9054303MXA
PACKAGE
40 Ld PDIP
44 Ld PLCC
40 Ld CERDIP
SMD#
44 Pad CLCC
SMD#
TEMPERATURE
RANGE
0oC to +70oC
-40oC to +85oC
0oC to +70oC
-40oC to +85oC
0oC to +70oC
-40oC to +85oC
-55oC to +125oC
-55oC to +125oC
PKG. NO.
E40.6
E40.6
N44.65
N44.65
F40.6
F40.6
F40.6
F40.6
J44.A
J44.A
CAUTION: These devices are sensitive to electrostatic discharge. Users should follow proper IC Handling Procedures.
Copyright © Harris Corporation 1997
4-192
File Number 2967.1
1 page ![]() ![]() 82C37A
Functional Description
The 82C37A direct memory access controller is designed to
improve the data transfer rate in systems which must
transfer data from an I/O device to memory, or move a block
of memory to an I/O device. It will also perform memory-to-
memory block moves, or fill a block of memory with data
from a single location. Operating modes are provided to
handle single byte transfers as well as discontinuous data
streams, which allows the 82C37A to control data movement
with software transparency.
The DMA controller is a state-driven address and control
signal generator, which permits data to be transferred
directly from an I/O device to memory or vice versa without
ever being stored in a temporary register. This can greatly
increase the data transfer rate for sequential operations,
compared with processor move or repeated string
instructions. Memory-to-memory operations require
temporary internal storage of the data byte between
generation of the source and destination addresses, so
memory-to-memory transfers take place at less than half the
rate of I/O operations, but still much faster than with central
processor techniques. The maximum data transfer rates
obtainable with the 82C37A are shown in Figure 1.
The block diagram of the 82C37A is shown on page 2. The
timing and control block, priority block, and internal registers
are the main components. Figure 2 lists the name and size
of the internal registers. The timing and control block derives
internal timing from clock input, and generates external
control signals. The Priority Encoder block resolves priority
contention between DMA channels requesting service
simultaneously.
For example, if a block of data is to be transferred from RAM
to an I/O device, the starting address of the data is loaded
into the 82C37A Current and Base Address registers for a
particular channel, and the length of the block is loaded into
the channel’s Word Count register. The corresponding Mode
register is programmed for a memory-to-I/O operation (read
transfer), and various options are selected by the Command
register and the other Mode register bits. The channel’s
mask bit is cleared to enable recognition of a DMA request
(DREQ). The DREQ can either be a hardware signal or a
software command.
Once initiated, the block DMA transfer will proceed as the
controller outputs the data address, simultaneous MEMR
and IOW pulses, and selects an I/O device via the DMA
acknowledge (DACK) outputs. The data byte flows directly
from the RAM to the I/O device. After each byte is
transferred, the address is automatically incremented (or
decremented) and the word count is decremented. The
operation is then repeated for the next byte. The controller
stops transferring data when the Word Count register
underflows, or an external EOP is applied.
NAME
Base Address Registers
Base Word Count Registers
Current Address Registers
Current Word Count Registers
SIZE NUMBER
16-Bits
4
16-Bits
4
16-Bits
4
16-Bits
4
82C37A
TRANSFER
TYPE
5MHz 8MHz 12.5MHz
UNIT
Compressed
2.50 4.00
6.25 MByte/sec
Normal I/O
1.67 2.67
4.17 MByte/sec
Memory-to-
Memory
0.63 1.00
1.56 MByte/sec
FIGURE 1. DMA TRANSFER RATES
DMA Operation
In a system, the 82C37A address and control outputs and
data bus pins are basically connected in parallel with the
system busses. An external latch is required for the upper
address byte. While inactive, the controller’s outputs are in a
high impedance state. When activated by a DMA request
and bus control is relinquished by the host, the 82C37A
drives the busses and generates the control signals to
perform the data transfer. The operation performed by
activating one of the four DMA request inputs has previously
been programmed into the controller via the Command,
Mode, Address, and Word Count registers.
Temporary Address Register
16-Bits
1
Temporary Word Count Register
16-Bits
1
Status Register
8-Bits
1
Command Register
8-Bits
1
Temporary Register
8-Bits
1
Mode Registers
6-Bits
4
Mask Register
4-Bits
1
Request Register
4-Bits
1
FIGURE 2. 82C37A INTERNAL REGISTERS
To further understand 82C37A operation, the states
generated by each clock cycle must be considered. The
DMA controller operates in two major cycles, active and idle.
After being programmed, the controller is normally idle until
a DMA request occurs on an unmasked channel, or a
software request is given. The 82C37A will then request
control of the system busses and enter the active cycle. The
active cycle is composed of several internal states,
depending on what options have been selected and what
type of operation has been requested.
4-196
5 Page ![]() ![]() 82C37A
Software Commands
There are special software commands which can be
executed by reading or writing to the 82C37A. These com-
mands do not depend on the specific data pattern on the
data bus, but are activated by the I/O operation itself. On
read type commands, the data value is not guaranteed.
These commands are:
Clear First/Last Flip-Flop - This command is executed
prior to writing or reading new address or word count infor-
mation to the 82C37A. This command initializes the flip-flop
to a known state (low byte first) so that subsequent accesses
to register contents by the microprocessor will address
upper and lower bytes in the correct sequence.
Set First/Last Flip-Flop - This command will set the flip-flop
to select the high byte first on read and write operations to
address and word count registers.
Master Clear - This software instruction has the same effect
as the hardware Reset. The Command, Status, Request,
and Temporary registers, and Internal First/Last Flip-Flop
and mode register counter are cleared and the Mask register
is set. The 82C37A will enter the idle cycle.
Clear Mask Register - This command clears the mask bits
of all four channels, enabling them to accept DMA requests.
Clear Mode Register Counter - Since only one address
location is available for reading the Mode registers, an inter-
nal two-bit counter has been included to select Mode regis-
ters during read operation. To read the Mode registers, first
execute the Clear Mode Register Counter command, then
do consecutive reads until the desired channel is read. Read
order is channel 0 first, channel 3 last. The lower two bits on
all Mode registers will read as ones.
External EOP Operation
The EOP pin is a bidirectional, open drain pin which may be
driven by external signals to terminate DMA operation.
Because EOP is an open drain pin an external pull-up resis-
tor to VCC is required. The value of the external pull-up
resistor used should guarantee a rise time of less than
125ns. It is important to note that the 82C37A will not accept
external EOP signals when it is in a SI (Idle) state. The
controller must be active to latch EXT EOP. Once latched,
the EXT EOP will be acted upon during the next S2 state,
unless the 82C37A enters an idle state first. In the latter
case, the latched EOP is cleared. External EOP pulses
occurring between active DMA transfers in demand mode
will not be recognized, since the 82C37A is in an SI state.
CHANNEL
REGISTER
0 Base and Current Address
Current Address
Base and Current Word
Count
Current Word Count
1 Base and Current Address
Current Address
Base and Current Word
Count
Current Word Count
2 Base and Current Address
Current Address
Base and Current Word
Count
Current Word Count
3 Base and Current Address
Current Address
Base and Current Word
Count
Current Word Count
SIGNALS
FIRST/LAST
FLIP-FLOP
OPERATION CS IOR IOW A3 A2 A1 A0
STATE
Write
Read
Write
Read
0100000
0100000
0010000
0010000
0100001
0100001
0010001
0010001
0
1
0
1
0
1
0
1
Write
Read
Write
Read
0100010
0100010
0010010
0010010
0100011
0100011
0010011
0010011
0
1
0
1
0
1
0
1
Write
Read
Write
Read
0100100
0100100
0010100
0010100
0100101
0100101
0010101
0010101
0
1
0
1
0
1
0
1
Write
Read
Write
Read
0100110
0100110
00101100
00101101
01001110
01001111
00101110
00101111
0
1
FIGURE 5. WORD COUNT AND ADDRESS REGISTER COMMAND CODES
DATA
BUS
DB0-DB7
A0-A7
A8-A15
A0-A7
A8-A15
W0-W7
W8-W15
W0-W7
W8-W15
A0-A7
A8-A15
A0-A7
A8-A15
W0-W7
W8-W15
W0-W7
W8-W15
A0-A7
A8-A15
A0-A7
A8-A15
W0-W7
W8-W15
W0-W7
W8-W15
A0-A7
A8-A15
A0-A7
A8-A15
W0-W7
W8-W15
W0-W7
W8-W15
4-202
11 Page |
Páginas | Total 23 Páginas | |
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