82C237
March 1997
CMOS High Performance
Programmable DMA Controller
Description
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 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 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).
Features
• Fully Compatible with Intersil 82C37A
- 82C237 May be Used in 8MHz and 12.5MHz 82C37A
Sockets
• Optimized for 10MHz and 12.5MHz 80C286 Systems
• Special Mode Permits 16-Bit, Zero Wait State DMA
Transfers
• High Speed Data Transfers:
- Up to 6.25MBytes/sec with 12.5MHz Clock in
Normal Mode
- Up to 12.5MBytes/sec with 12.5MHz Clock in 16-Bit
Mode
• Compatible with the NMOS 8237A
• Four Independent Maskable Channels with Autoinitial-
ization Capability
• Cascadable to any Number of Channels
• 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
Ordering Information
PACKAGE
PDIP
TEMPERATURE
RANGE
0
o
C to +70
o
C
-40
o
C to +85
o
C
PLCC
0
o
C to +70
o
C
-40
o
C to +85
o
C
SBDIP
0
o
C to +70
o
C
-40
o
C to +85
o
C
-55
o
C to +125
o
C
SMD#
CLCC
SMD#
-55
o
C to +125
o
C
8MHz
CP82C237
IP82C237
CS82C237
IS82C237
CD82C237
ID82C237
MD82C237/B
5962-9054304MQA
MR82C237/B
5962-9054304MXA
12.5MHz
CP82C237-12
IP82C237-12
CS82C237-12
IS82C237-12
CD82C237-12
ID82C237-12
MD82C237-12/B
5962-9054305MQA
MR82C237-12/B
5962-9054305MXA
E40.6
E40.6
N44.65
N44.65
F40.6
F40.6
F40.6
F40.6
J44.A
J44.A
PKG. NO.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
http://www.intersil.com or 407-727-9207
|
Copyright
©
Intersil Corporation 1999
File Number
2965.1
4-148
82C237
Pinouts
82C237 (DIP)
TOP VIEW
IOR
IOW
MEMR
MEMW
DWLE
(NOTE)
READY
HLDA
ADSTB
AEN
HRQ
CS
CLK
RESET
DACK2
DACK3
DREQ3
DREQ2
DREQ1
DREQ0
(GND) VSS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
40 A7
39 A6
38 A5
37 A4
36 EOP
35 A3
34 A2
33 A1
32 A0
31 V
CC
30 DB0
29 DB1
28 DB2
27 DB3
26 DB4
25 DACK0
24 DACK1
23 DB5
22 DB6
21 DB7
NC 7
NC 8
HLDA 9
ADSTB 10
AEN 11
HRQ 12
CS 13
CLK 14
RESET 15
DACK2 16
NC 17
18 19 20 21 22 23 24 25 26 27 28
DREQ3
DREQ2
DREQ1
DREQ0
GND
DB7
DB6
DACK3
DB5
DACK1
DACK0
82C237 (CLCC/PLCC)
TOP VIEW
READY
DWLE
(NOTE)
MEMW
MEMR
EOP
39 A3
38 A2
37 A1
36 A0
35 V
CC
34 DB0
33 DB1
32 DB2
31 DB3
30 DB4
29 NC
IOW
IOR
A7
A6
A5
6
5
4
3
2
1 44 43 42 41 40
NOTE: See Pin Description.
Block Diagram
DWLE
EOP
RESET
CS
READY
CLK
AEN
ADSTB
MEMR
MEMW
IOR
IOW
READ BUFFER
BASE
ADDRESS
(16)
BASE
WORD
COUNT
(16)
TIMING
AND
CONTROL
DECREMENTOR
TEMP WORD
COUNT REG (16)
16-BIT BUS
16-BIT BUS
READ WRITE BUFFER
CURRENT
ADDRESS
(16)
CURRENT
WORD
COUNT
(16)
OUTPUT
BUFFER
A4 - A7
INC DECREMENTOR
TEMP ADDRESS
REG (16)
IO
BUFFER
A0 - A3
A8 - A15
COMMAND
CONTROL
DATA-WIDTH
(4)
DREQ0 -
DREQ3
HLDA
HRQ
DACK0 -
DACK3
4
4
PRIORITY
ENCODER
AND
ROTATING
PRIORITY
LOGIC
COMMAND
(8)
MASK
(4)
REQUEST
(4)
WRITE
BUFFER
READ
BUFFER
D0 - D1
A4
INTERNAL DATA BUS
IO
BUFFER
DB0 - DB7
MODE
(4 x 6)
STATUS
(8)
TEMPORARY
(8)
4-149
82C237
Pin Description
SYMBOL
V
CC
PIN
NUMBER
31
TYPE
DESCRIPTION
V
CC
: is the +5V power supply pin. A 0.1µF capacitor between pins 31 and 20 is recommended for
decoupling.
Ground
I
CLOCK INPUT: The Clock Input is used to generate the timing signals which control 82C237
operations. This input may be driven from DC to 12.5MHz for the 82C237-12 or from DC to 8MHz
for the 82C237. The Clock may be stopped in either state for standby operation.
CHIP SELECT: Chip Select is an active low input used to enable the controller onto the data bus for
CPU communications.
RESET: This is an active high input which clears the Command, Status, Request, and Temporary
registers, the First/Last Flip-Flop, and the mode register counter. The Mask register is set to ignore
requests. The Data-Width register is set to perform 8-bit transfers on all channels (82C237 only).
Following a Reset, the controller is in an idle cycle.
READY: This signal can be used to extend the memory read and write pulses from the 82C237 to
accommodate slow memories or I/O devices. READY must not make transitions during its specified
set-up and hold times. See Figure 14 for timing. READY is ignored in verify transfer mode.
HOLD ACKNOWLEDGE: The active high Hold Acknowledge from the CPU indicates that it has
relinquished control of the system busses. HLDA is a synchronous input and must not transition
during its specified set-up time. There is an implied hold time (HLDA inactive) of TCH from the rising
edge of clock, during which time HLDA must not transition.
DMA REQUEST: The DMA Request (DREQ) lines are individual asynchronous channel request
inputs used by peripheral circuits to obtain DMA service. In Fixed Priority, DREQ0 has the highest
priority and DREQ3 has the lowest priority. A request is generated by activating the DREQ line of a
channel. DACK will acknowledge the recognition of a DREQ signal. Polarity of DREQ is
programmable. RESET initializes these lines to active high. DREQ must be maintained until the
corresponding DACK goes active. DREQ will not be recognized while the clock is stopped. Unused
DREQ inputs should be pulled High or Low (inactive) and the corresponding mask bit set. In 16-bit
Transfer mode (82C237 only), each DREQ channel may be programmed to perform either 8-bit or
16-bit DMA transfers.
DATA BUS: The Data Bus lines are bidirectional three-state signals connected to the system data
bus. The outputs are enabled in the Program condition during the I/O Read to output the contents
of a register to the CPU. The outputs are disabled and the inputs are read during an I/O Write cycle
when the CPU is programming the 82C237 control registers. During DMA cycles, the most signifi-
cant 8-bits of the address are output onto the data bus to be strobed into an external latch by ADSTB.
In memory-to-memory operations, data from the memory enters the 82C237 on the data bus during
the read-from-memory transfer, then during the write-to-memory transfer, the data bus outputs write
the data into the new memory location.
I/O READ: I/O Read is a bidirectional active low three-state line. In the Idle cycle, it is an input con-
trol signal used by the CPU to read the control registers. In the Active cycle, it is an output control
signal used by the 82C237 to access data from the peripheral during a DMA Write transfer.
I/O WRITE: I/O Write is a bidirectional active low three-state line. In the Idle cycle, it is an input con-
trol signal used by the CPU to load information into the 82C237. In the Active cycle, it is an output
control signal used by the 82C237 to load data to the peripheral during a DMA Read transfer.
GND
CLK
20
12
CS
11
I
RESET
13
I
READY
6
I
HLDA
7
I
DREQ0-
DREQ3
16-19
I
DB0-DB7
21-23
26-30
I/O
IOR
1
I/O
IOW
2
I/O
4-150
82C237
Pin Description
SYMBOL
EOP
PIN
NUMBER
36
(Continued)
TYPE
I/O
DESCRIPTION
END OF PROCESS: End of Process (EOP) is an active low bidirectional signal. Information
concerning the completion of DMA services is available at the bidirectional EOP pin.
The 82C237 allows an external signal to terminate an active DMA service by pulling the EOP pin
low. A pulse is generated by the 82C237 when terminal count (TC) for any channel is reached,
except for channel 0 in memory-to-memory mode. During memory-to-memory transfers, EOP will
be output when the TC for channel 1 occurs.
The EOP pin is driven by an open drain transistor on-chip, and requires an external pull-up resistor
to V
CC
.
When an EOP pulse occurs, whether internally or externally generated, the 82C237 will terminate
the service, and if autoinitialize is enabled, the base registers will be written to the current registers
of that channel. The mask bit and TC bit in the status word will be set for the currently active channel
by EOP unless the channel is programmed for autoinitialize. In that case, the mask bit remains clear.
A0-A3
32-35
I/O
ADDRESS: The four least significant address lines are bidirectional three-state signals. In the Idle
cycle, they are inputs and are used by the 82C237 to address the control register to be loaded or
read. In the Active cycle, they are outputs and provide the lower 4-bits of the output address. When
in 16-bit mode (82C237 only), and the active channel is a 16-bit channel (as defined by the Data-
Width register), then A0 will remain low during the entire transfer (i.e. an even word address will al-
ways be generated).
ADDRESS: The four most significant address lines are three-state outputs and provide 4-bits of
address. These lines are enabled only during the DMA service.
HOLD REQUEST: The Hold Request (HRQ) output is used to request control of the system bus.
When a DREQ occurs and the corresponding mask bit is clear, or a software DMA request is made,
the 82C237 issues HRQ. The HLDA signal then informs the controller when access to the system
busses is permitted. For stand-alone operation where the 82C237 always controls the busses, HRQ
may be tied to HLDA. This will result in one S0 state before the transfer.
DMA ACKNOWLEDGE: DMA acknowledge is used to notify the individual peripherals when one
has been granted a DMA cycle. The sense of these lines is programmable. RESET initializes them
to active low.
ADDRESS ENABLE: Address Enable enables the 8-bit latch containing the upper 8 address bits
onto the system address bus. AEN can also be used to disable other system bus drivers during DMA
transfers. AEN is active HIGH.
ADDRESS STROBE: This is an active high signal used to control latching of the upper address
byte. It will drive directly the strobe input of external transparent octal latches, such as the 82C82.
During block operations, ADSTB will only be issued when the upper address byte must be updated,
thus speeding operation through elimination of S1 states. ADSTB timing is referenced to the falling
edge of the 82C237 clock.
MEMORY READ: The Memory Read signal is an active low three-state output used to access data
from the selected memory location during a DMA Read or a memory-to-memory transfer.
MEMORY WRITE: The Memory Write is an active low three-state output used to write data to the
selected memory location during a DMA Write or a memory-to-memory transfer.
DATA-WIDTH, LATCH ENABLE: In normal 8-bit transfer mode (16-bit transfer mode not enabled),
this output is always high impedance three-stated. In 16-bit transfer mode (82C237 only), this output
serves a dual purpose. During S1 cycles, the DWLE output indicates the data width (0 = 16-bit, 1 =
8-bit) of the active channel. During memory-to-memory transfers, the DWLE output is used to enable
an external latch which temporarily stores the 8 most significant bits of data during the read-from-
memory transfer. DWLE enables this byte of data onto the data bus during the write-to-memory
transfer of a memory-to-memory operation.
A4-A7
37-40
O
HRQ
10
O
DACK0-
DACK3
14, 15
24, 25
O
AEN
9
O
ADSTB
8
O
MEMR
3
O
MEMW
4
O
DWLE
5
O
4-151
82C237
Functional Description
The 82C237 is an improved version of the Intersil 82C37A
DMA controller and is fully software and pin for pin compati-
ble with the 82C37A. All operational and pin descriptions of
the 82C37A apply to the 82C237 with additional features
noted in the section titled 82C237 Operation.
The 82C237 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 82C237 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 82C237 are shown in Figure 1.
The block diagram of the 82C237 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 CLK input, and generates external
control signals. The Priority Encoder block resolves priority
contention between DMA channels requesting service
simultaneously.
82C237
TRANSFER
TYPE
Compressed
Normal I/O
Memory-to-
Memory
8MHz
8-BIT
4.00
2.67
1.00
16-BIT
8.00
5.34
2.00
12.5MHz
8-BIT
6.25
4.17
1.56
16-BIT
12.5
8.34
3.12
UNIT
MByte/sec
MByte/sec
MByte/sec
been programmed into the controller via the Command,
Mode, Address, and Word Count registers.
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 82C237 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
Temporary Address Register
Temporary Word Count Register
Status Register
Command Register
Temporary Register
Mode Registers
Mask Register
Request Register
Data-Width Register (See Note)
NOTE: 82C237 only
SIZE
16-Bits
16-Bits
16-Bits
16-Bits
16-Bits
16-Bits
8-Bits
8-Bits
8-Bits
6-Bits
4-Bits
4-Bits
4-Bits
NUMBER
4
4
4
4
1
1
1
1
1
4
1
1
1
FIGURE 1. DMA TRANSFER RATES
FIGURE 2. 82C237 INTERNAL REGISTERS
DMA Operation
In a system, the 82C237 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 82C237
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
To further understand 82C237 operation, the states
generated by each CLK 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 82C237 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.
4-152
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