COM20020D
COM20020 ULANC
Revision D
Universal Local Area Network Controller
with 2K x 8 On-Board RAM
FEATURES
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New Features for Rev. D
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Data Rates up to 5 Mbps
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Programmable Reconfiguration Times
24 Pin DIP, 28 Pin PLCC Package
Ideal for Industrial/Factory/Building
Automation and Transportation
Applications
Deterministic, (ANSI 878.1), Token Passing
ARCNET Protocol
Minimal Microcontroller and Media
Interface Logic Required
Flexible Interface For Use With All
Microcontrollers or Microprocessors
Automatically Detects Type of
Microcontroller Interface
2Kx8 On-Chip Dual Port RAM
Command Chaining for Packet Queuing
Sequential Access to Internal RAM
Software Programmable Node ID
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Eight, 256 Byte Pages Allow Four Pages TX
and RX Plus Scratch-Pad Memory
Next ID Readable
Internal Clock Scaler and Clock Multiplier for
Adjusting Network Speed
Operating Temperature Range of -40
o
C to
+85
o
C
Self-Reconfiguration Protocol
Supports up to 255 Nodes
Supports Various Network Topologies (Star,
Tree, Bus...)
CMOS, Single +5V Supply
Duplicate Node ID Detection
Powerful Diagnostics
Receive All Packets Mode
Flexible Media Interface:
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Traditional Hybrid Interface For Long
Distances up to Four Miles at 2.5Mbps.
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RS485 Differential Driver Interface For
Low Cost, Low Power, High Reliability
GENERAL DESCRIPTION
SMSC's COM20020D is a member of the family of
Embedded ARCNET Controllers from Standard
Microsystems Corporation. The device is a
general purpose communications controller for
networking microcontrollers and intelligent
peripherals in industrial, automotive, and
embedded control
environments
using an
®
ARCNET
protocol engine. The small 24 pin
package, flexible microcontroller and media
interfaces, eight- page message support, and
extended temperature range of the COM20020D
make it the only true network controller optimized
for use in industrial, embedded, and automotive
applications. Using an ARCNET protocol engine
is the ideal solution for embedded control
applications because it provides a deterministic
token-passing protocol, a highly reliable and
proven networking scheme, and a data rate of up
to 5 Mbps when using the COM20020D.
A token-passing protocol provides predictable
response times because each network event
occurs within a predetermined time interval, based
upon the number of nodes on the network. The
deterministic nature of ARCNET is essential in
real time applications. The integration of the 2Kx8
RAM buffer on-chip, the Command Chaining
feature, the 5 Mbps maximum data rate, and the
internal diagnostics make the COM20020D the
highest performance embedded communications
device available. With only one COM20020D and
one microcontroller, a complete communications
node may be implemented.
ARCNET is a registered trademark of Datapoint Corporation
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TABLE OF CONTENTS
FEATURES ....................................................................................................................................... 1
GENERAL DESCRIPTION ................................................................................................................ 1
PIN CONFIGURATION ...................................................................................................................... 4
DESCRIPTION OF PIN FUNCTIONS................................................................................................. 5
PROTOCOL DESCRIPTION.............................................................................................................. 8
NETWORK PROTOCOL ............................................................................................................... 8
DATA RATES ............................................................................................................................... 8
NETWORK RECONFIGURATION ................................................................................................. 9
BROADCAST MESSAGES.......................................................................................................... 10
EXTENDED TIMEOUT FUNCTION ............................................................................................. 10
LINE PROTOCOL ....................................................................................................................... 10
SYSTEM DESCRIPTION ................................................................................................................. 13
MICROCONTROLLER INTERFACE............................................................................................ 13
TRANSMISSION MEDIA INTERFACE......................................................................................... 17
FUNCTIONAL DESCRIPTION ......................................................................................................... 22
MICROSEQUENCER.................................................................................................................. 22
INTERNAL REGISTERS ............................................................................................................. 25
INTERNAL RAM ......................................................................................................................... 38
COMMAND CHAINING ............................................................................................................... 43
INITIALIZATION SEQUENCE...................................................................................................... 45
IMPROVED DIAGNOSTICS ........................................................................................................ 46
OPERATIONAL DESCRIPTION ...................................................................................................... 49
MAXIMUM GUARANTEED RATINGS* ........................................................................................ 49
DC ELECTRICAL CHARACTERISTICS....................................................................................... 49
TIMING DIAGRAMS........................................................................................................................ 52
APPENDIX A................................................................................................................................... 67
APPENDIX B: EXAMPLE OF INTERFACE CIRCUIT DIAGRAM TO ISA BUS ................................ 71
APPENDIX C................................................................................................................................... 72
SOFTWARE IDENTIFICATION OF THE COM20020 REV B, REV C AND REV D ............................ 72
For more details on the ARCNET protocol engine and traditional dipulse signaling schemes,
please refer to the ARCNET Local Area Network Standard, available from Standard Microsystems
Corporation or the ARCNET Designer's Handbook, available from Datapoint Corporation.
For more detailed information on cabling options including RS485, transformer-coupled RS-485
and Fiber Optic interfaces, please refer to the following technical note which is available from
Standard Microsystems Corporation: Technical Note 7-5 - Cabling Guidelines for the COM20020
ULANC.
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PIN CONFIGURATION
nRESET IN
A1
A2/ALE
AD0
AD1
AD2
D3
D4
D5
D6
D7
VSS
2
3
4
5
6
7
8
9
10
11
12
23
22
21
20
19
18
17
16
15
14
13
nRD/nDS
nWR/DIR
nWR/DIR
nCS
nINTR
nRESET IN
nTXEN
RXIN
nPULSE2
A2/ALE
nPULSE1
AD0
XTAL2
XTAL1
4
5
6
7
8
9
10
11
12
D7
3
13
N/C
nRD/nDS
VDD
A0/nMUX
A1
27
28
1
2
17
16
15
14
XTAL2
XTAL1
VDD
VSS
26
25
24
23
22
21
20
19
18
nPULSE 1
AD1
nCS
A0/nMUX
AD2
D3
VSS
1
24
VDD
D4
D5
Packages: 24-Pin DIP or 28-Pin PLCC
Ordering Information:
COM20020 I
P
PACKAGE TYPE: P = Plastic, LJP = PLCC
TEMP RANGE:
(Blank) = Commercial: 0°C to +70°C
I = Industrial: -40°C to +85°C
DEVICE TYPE: 20020 = Universal Local Area Network Controller
(with 2K x 8 RAM)
4
VSS
D6
nPULSE2
nTXEN
nINTR
RXIN
DESCRIPTION OF PIN FUNCTIONS
DIP PIN
NO.
PLCC PIN
NO.
NAME
SYMBOL
DESCRIPTION
MICROCONTROLLER INTERFACE
1-3
1-3
Address
0-2
A0/nMUX,
A1,A2/ALE
Input. On a non-multiplexed mode, A0-A2
are address input bits. (A0 is the LSB) On a
multiplexed address/data bus, nMUX tied
Low, A1 is left open, and ALE is tied to the
Address Latch Enable signal. A1 is
connected to an internal pull-up resistor.
Input/Output. On a non-multiplexed bus,
these signals are used as the data lines for
the device. On a multiplexed address/data
bus, AD0-AD2 act as the address lines
(latched by ALE) and as the low data lines for
the device. D3-D7 are always used for data
only. These signals are connected to internal
pull-up resistors.
Input. On a 68XX-like bus, nDS is an active
low signal issued by the microcontroller as the
data strobe signal to strobe the data onto the
bus. On a 80XX-like bus, nRD is an active
low signal issued by the microcontroller to
indicate a read operation.
Input. On a 68XX-like bus, DIR is issued by
the microcontroller as the Read/nWrite signal
to determine the direction of data transfer. In
this case, a logic "1" selects a read operation,
while a logic "0" selects a write operation. In
this case, data is actually strobed by the nDS
signal. On an 80XX-like bus, nWR is an
active low signal issued by the microcontroller
to indicate a write operation. In this case, a
logic "0" on this pin, when the COM20020D is
accessed, enables data from the data bus to
be written to the device.
Input. This active low signal executes a
hardware reset.
Output. This active low signal is generated by
the COM20020D when an enabled interrupt
condition occurs.
Input. This active low signal selects the
COM20020D for an access.
5
4-11
4-6,8-12
Data 0-7
AD0-AD2,
D3-D7
23
27
nRead/nData nRD/nDS
Strobe
22
26
nWrite/
Direction
nWR/DIR
19
20
23
24
nReset in
nInterrupt
nRESET
nINTR
21
25
nChip Select
nCS
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