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PDF COM20019I Data sheet ( Hoja de datos )
| Número de pieza | COM20019I | |
| Descripción | Low Cost ARCNET (ANSI 878.1) Controller | |
| Fabricantes | SMSC Corporation | |
| Logotipo |  |
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Product Features
New Features:
− Data Rates up to 312.5 Kbps
− Programmable Reconfiguration Times
28 Pin PLCC and 48 Pin TQFP Packages;
Green, Lead-free Packages also Available
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
COM20019I
Low Cost ARCNET
(ANSI 878.1)
Controller with 2K x 8
On-Board RAM
Datasheet
Eight, 256 Byte Pages Allow Four Pages TX and
RX Plus Scratch-Pad Memory
Next ID Readable
Internal Clock Scaler for Adjusting Network
Speed
Operating Temperature Range of -40oC to +85oC
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:
− RS485 Differential Driver Interface For Low Cost,
Low Power, High Reliability
ORDERING INFORMATION
Order Number(s):
COM20019ILJP for 28 pin PLCC package; COM20019I-DZD for 28 pin PLCC package (green, lead-free)
COM20019I-HD for 48 pin TQFP package; COM20019I-HT for 48 pin TQFP package (green, lead-free)
SMSC COM20019I
Page 1
DATASHEET
Rev. 03-07-06
1 page  
Low Cost ARCNET (ANSI 878.1) Controller with 2K x 8 On-Board RAM
Chapter 1 GENERAL DESCRIPTION
SMSC's COM20019I 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 flexible microcontroller and media interfaces, eight- page message
support, and extended temperature range of the COM20019I 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 312.5 Kbps
when using the COM20019I.
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 maximum data rate, and the internal diagnostics make the COM20019I
the highest performance embedded communications device available. With only one COM20019I and one
microcontroller, a complete communications node may be implemented.
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.
SMSC COM20019I
Page 5
DATASHEET
Rev. 03-07-06
5 Page 
Low Cost ARCNET (ANSI 878.1) Controller with 2K x 8 On-Board RAM
Chapter 4 PROTOCOL DESCRIPTION
4.1
NETWORK PROTOCOL
Communication on the network is based on a token passing protocol. Establishment of the network
configuration and management of the network protocol are handled entirely by the COM20019I's internal
microcoded sequencer. A processor or intelligent peripheral transmits data by simply loading a data packet
and its destination ID into the COM20019I's internal RAM buffer, and issuing a command to enable the
transmitter. When the COM20019I next receives the token, it verifies that the receiving node is ready by
first transmitting a FREE BUFFER ENQUIRY message. If the receiving node transmits an ACKnowledge
message, the data packet is transmitted followed by a 16-bit CRC. If the receiving node cannot accept the
packet (typically its receiver is inhibited), it transmits a Negative AcKnowledge message and the
transmitter passes the token. Once it has been established that the receiving node can accept the packet
and transmission is complete, the receiving node verifies the packet. If the packet is received
successfully,
the receiving node transmits an ACKnowledge message (or nothing if it is not received successfully)
allowing the transmitter to set the appropriate status bits to indicate successful or unsuccessful delivery of
the packet. An interrupt mask permits the COM20019I to generate an interrupt to the processor when
selected status bits become true. Figure 3.1 - COM20019I OPERATION is a flow chart illustrating the
internal operation of the COM20019I connected to a 20 MHz crystal oscillator.
4.2 DATA RATES
The COM20019I is capable of supporting data rates from 156.25 Kbps to 312.5 Kbps. The following
protocol description assumes a 312.5 Kbps data rate. For slower data rates, an internal clock divider
scales down the clock frequency. Thus all timeout values are scaled as shown in the following table:
Example: IDLE LINE Timeout @ 312.5 Kbps = 656 μs. IDLE LINE Timeout for 156.2 Kbps is 656 μs * 2 =
1.3 ms
INTERNAL CLOCK
FREQUENCY
20 MHz
CLOCK
PRESCALER
Div. by 64
Div. by 128
DATA RATE
312.5 Kbps
156.25 Kbps
TIMEOUT SCALING FACTOR
(MULTIPLY BY)
1
2
4.3
NETWORK RECONFIGURATION
A significant advantage of the COM20019I is its ability to adapt to changes on the network. Whenever a
new node is activated or deactivated, a NETWORK RECONFIGURATION is performed. When a new
COM20019I is turned on (creating a new active node on the network), or if the COM20019I has not
received an INVITATION TO TRANSMIT for 6.72S, or if a software reset occurs, the COM20019I causes a
NETWORK RECONFIGURATION by sending a RECONFIGURE BURST consisting of eight marks and
one space repeated 765 times. The purpose of this burst is to terminate all activity on the network. Since
this burst is longer than any other type of transmission, the burst will interfere with the next INVITATION
TO TRANSMIT, destroy the token and keep any other node from assuming control of the line.
When any COM20019I senses an idle line for greater than 656μS, which occurs only when the token Is
lost, each COM20019I starts an internal timeout equal to 1.168mS times the quantity 255 minus its own
ID. The COM20019I starts network reconfiguration by sending an invitation to transmit first to itself and
then to all other nodes by decrementing the destination Node ID. If the timeout expires with no line
SMSC COM20019I
Page 11
DATASHEET
Rev. 03-07-06
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet COM20019I.PDF ] | |
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