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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

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Pinouts
82C37A (PDIP/CERDIP)
TOP VIEW
IOR 1
IOW 2
MEMR 3
MEMW 4
NC 5
READY 6
HLDA 7
ADSTB 8
AEN 9
HRQ 10
CS 11
CLK 12
RESET 13
DACK2 14
DACK3 15
DREQ3 16
DREQ2 17
DREQ1 18
DREQ0 19
(GND) VSS 20
40 A7
39 A6
38 A5
37 A4
36 EOP
35 A3
34 A2
33 A1
32 A0
31 VCC
30 DB0
29 DB1
28 DB2
27 DB3
26 DB4
25 DACK0
24 DACK1
23 DB5
22 DB6
21 DB7
82C37A
82C37A (CLCC/PLCC)
TOP VIEW
6 5 4 3 2 1 44 43 42 41 40
NC 7
39 A3
NC 8
38 A2
HLDA 9
37 A1
ADSTB 10
36 A0
AEN 11
35 VCC
HRQ 12
34 DB0
CS 13
33 DB1
CLK 14
32 DB2
RESET 15
31 DB3
DACK2 16
NC 17
30 DB4
29 NC
18 19 20 21 22 23 24 25 26 27 28
Block Diagram
EOP
RESET
CS
READY
CLK
AEN
ADSTB
MEMR
MEMW
IOR
IOW
TIMING
AND
CONTROL
DREQ0 -
DREQ3
HLDA
HRQ
DACK0 -
DACK3
4
4
PRIORITY
ENCODER
AND
ROTATING
PRIORITY
LOGIC
DECREMENTOR
TEMP WORD
COUNT REG (16)
INC/DECREMENTOR
TEMP ADDRESS
REG (16)
16-BIT BUS
16-BIT BUS
READ BUFFER
READ WRITE BUFFER
BASE
ADDRESS
(16)
BASE
WORD
COUNT
(16)
CURRENT
ADDRESS
(16)
CURRENT
WORD
COUNT
(16)
WRITE
BUFFER
READ
BUFFER
IO
BUFFER
A0 - A3
OUTPUT
BUFFER
A4 - A7
COMMAND
CONTROL
D0 - D1
COMMAND
(8)
MASK
(4)
REQUEST
(4)
INTERNAL DATA BUS
IO
BUFFER
MODE
(4 x 6)
STATUS
(8)
TEMPORARY
(8)
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82C37A
Pin Description
PIN
SYMBOL NUMBER TYPE
DESCRIPTION
VCC
31
VCC: is the +5V power supply pin. A 0.1µF capacitor between pins 31 and 20 is recommended for
decoupling.
GND
20
Ground
CLK 12 I CLOCK INPUT: The Clock Input is used to generate the timing signals which control 82C37A
operations. This input may be driven from DC to 12.5MHz for the 82C37A-12, from DC to 8MHz for
the 82C37A, or from DC to 5MHz for the 82C37A-5. The Clock may be stopped in either state for
standby operation.
CS 11 I CHIP SELECT: Chip Select is an active low input used to enable the controller onto the data bus for
CPU communications.
RESET
13
READY
6
HLDA
7
DREQ0-
DREQ3
16-19
DB0-DB7
21-23
26-30
IOR 1
IOW 2
I 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. Following a Reset, the controller is in an idle cycle.
I READY: This signal can be used to extend the memory read and write pulses from the 82C37A to
accommodate slow memories or I/O devices. READY must not make transitions during its specified
set-up and hold times. See Figure 12 for timing. READY is ignored in verify transfer mode.
I 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 CLK, during which time HLDA must not transition.
I 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.
I/O 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 82C37A 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 82C37A 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 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 82C37A to access data from the peripheral during a DMA Write transfer.
I/O 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 82C37A. In the Active cycle, it is an output
control signal used by the 82C37A to load data to the peripheral during a DMA Read transfer.
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82C37A
Pin Description (Continued)
PIN
SYMBOL NUMBER TYPE
DESCRIPTION
EOP
36 I/O 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 82C37A allows an external signal to terminate an active DMA service by pulling the EOP pin
low. A pulse is generated by the 82C37A 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 VCC.
When an EOP pulse occurs, whether internally or externally generated, the 82C37A 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 82C37A 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.
A4-A7
37-40
O 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.
HRQ 10 O 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 82C37A issues HRQ. The HLDA signal then informs the controller when access to the system
busses is permitted. For stand-alone operation where the 82C37A always controls the busses, HRQ
may be tied to HLDA. This will result in one S0 state before the transfer.
DACK0-
DACK3
14, 15
24, 25
O 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.
AEN 9 O 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.
ADSTB
8
O 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 82C37A clock.
MEMR
3
O 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.
MEMW
4
O MEMORY WRITE: The Memory Write signal 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.
NC 5
NO CONNECT: Pin 5 is open and should not be tested for continuity.
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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.
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