COM20020D

COM20020 3.3V

COM20020 3.3V ULANC

Universal Local Area Network Controller

with 2K x 8 On-Board RAM

FEATURES

New Features

Data Rates up to 5 Mbps

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

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

C to

+85

Self-Reconfiguration Protocol

Supports up to 255 Nodes

Supports Various Network Topologies (Star,

Tree, Bus...)

CMOS, Single +3.3V Supply

Duplicate Node ID Detection

Powerful Diagnostics

Receive All Packets Mode

Flexible Media Interface:

Traditional Hybrid Interface For Long

Distances up to Four Miles at 2.5Mbps.

RS485 Differential Driver Interface For

Low Cost, Low Power, High Reliability

ORDERING INFORMATION

Order Numbers:

COM20020ILJP3V

28 PLCC Package

COM20020IP3V

24 DIP Package

GENERAL DESCRIPTION

SMSC's COM20020 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 COM20020

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 COM20020.

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 COM20020 the

highest performance embedded communications

device available. With only one COM20020 and

one microcontroller, a complete communications

node may be implemented.

PIN CONFIGURATION

A0/nMUX

A2/ALE

AD0

AD1

AD2

nRD/nDS

nWR/DIR

nCS

nINTR

nRESET IN

nTXEN

RXIN

nPULSE2

nPULSE1

XTAL2

XTAL1

VDD

nPULSE

XTAL2

XTAL1

VDD

VSS

N/C

nWR/DIR

nRD/nD

VDD

A2/ALE

AD0

Packages: 24-Pin DIP or 28-Pin

Ordering

COM2002

VSS

A0/nMU

PACKAGE TYPE: P = Plastic, LJP =

TEMP RANGE:

I = Industrial: -40°C to

DEVICE TYPE: 20020 = Universal Local Area Network

(with 2K x 8

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.

4-11 4-6,8-12

Data

0-7

AD0-AD2,

D3-D7

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.

23 27 nRead/nData

Strobe

nRD/nDS

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.

22 26 nWrite/

Direction

nWR/DIR

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 COM20020 is

accessed, enables data from the data bus to

be written to the device.

nReset in

nRESET

Input. This active low signal executes a

hardware reset.

nInterrupt

nINTR

Output. This active low signal is generated by

the COM20020 when an enabled interrupt

condition occurs.

nChip Select nCS

Input. This active low signal selects the

COM20020 for an access.

TRANSMISSION MEDIA INTERFACE

DIP PIN

NO.

PLCC PIN

NO.

NAME

SYMBOL

DESCRIPTION

16,15 19,18 nPulse

nPulse 1

nPULSE2,

nPULSE1

Output (nPULSE1), Input/Output (nPULSE2).

In Normal Mode, these active low signals

carry the transmit data information, encoded

in pulse format, as DIPULSE waveform.

When the device is in Backplane Mode, the

nPULSE1 signal driver is programmable

(push/pull or open-drain), while the nPULSE2

signal provides a clock with frequency of

double the data rate. nPULSE1 is connected

to a weak internal pull-up resistor on the

open/drain driver in backplane mode.

Receive In

RXIN

Input. This signal carries the receive data

information from the line tranceiver.

18 21 nTransmit

nEnable

nTXEN

Output. This signal is used prior to the Power-

up to enable the line drivers for transmission.

The polarity of the signal is programmable

through the nPULSE2 pin.

nPULSE2 floating before Power-up: nTXEN

active low (Default option)

nPULSE2 grounded before Power-up:

nTXEN active high (This option is only

available in Backplane Mode)

13,14 16,17 Crystal

Oscillator

XTAL1,

XTAL2

An external crystal should be connected to

these pins. Oscillation frequency range is

from 10 to 20 MHz. If an external TTL clock is

used instead, it must be connected to XTAL1

with a 390

pull-up resistor, and XTAL2

should be left floating.

24 15,28

Power

Supply

+3.3 Volt Power Supply pin.

12 7,14,22

Ground

Ground pin.

FIGURE 1 - COM20020 OPERATION

Invitation

to Transmit to

this ID?

Free Buffer

Enquiry to

this ID?

SOH?

RI?

Write SID

to Buffer

DID

=0?

DID

=ID?

Write Buffer

with Packet

CRC

OK?

LENGTH

OK?

DID

=0?

DID

=ID?

SEND ACK

Broadcast

Enabled?

No Activity

for 41

uS?

Set NID=ID

Start Timer:

T=(255-ID)

Activity

On Line?

T=0?

Set RI

RI?

Transmit

NAK

Transmit

ACK

Set NID=ID

Write ID to

RAM Buffer

Send

Reconfigure

Burst

Power On

Reconfigure

Timer has

Timed Out

Start

Reconfiguration

Timer (420 mS)*

TA?

Broadcast?

Transmit

Free Buffer

Enquiry

Activity

Pass the

Token

Set TA

ACK?

NAK?

Activity

Increment

NID

Send

Packet

Was Packet

Broadcast?

Activity

ACK?

Set TMA

Set TA

x 73 us

for 37.4

us?

for 37.4

us?

for 37.4

us?

Read Node ID

ID refers to the identification number of the ID assigned to this node.

NID refers to the next identification number that receives the token

after this ID passes it.

SID refers to the source identification.

DID refers to the destination identification.

SOH refers to the start of header character; preceeds all data packets.

* Reconfig timer is programmable via setup2 register bits 1, 0.

Note - All time values are valid for 5 Mbps.

PROTOCOL DESCRIPTION

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

COM20020's internal microcoded sequencer. A

processor or intelligent peripheral transmits data

by simply loading a data packet and its destination

ID into the COM20020's internal RAM buffer, and

issuing a command to enable the transmitter.

When the COM20020 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 COM20020 to generate an

interrupt to the processor when selected status

bits become true. Figure 1 is a flow chart

illustrating the internal operation of the

COM20020 connected to a 20 MHz crystal

oscillator.

DATA RATES

The COM20020 is capable of supporting data

rates from 156.25 Kbps to 5 Mbps. The following

protocol description assumes a 5 Mbps data rate.

To attain the faster data rates, the clock frequency

may be doubled by the internal clock multiplier

(see next section). 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 @ 5 Mbps = 41

IDLE LINE Timeout for 156.2 Kbps is 41

s * 32 =

1.3 ms

INTERNAL

CLOCK

FREQUENCY

CLOCK

PRESCALER

DATA RATE

TIMEOUT SCALING

FACTOR (MULTIPLY BY)

40 MHz

Div. by 8

5 Mbps

20 MHz

Div. by 8

Div. by 16

Div. by 32

Div. by 64

Div. by 128

2.5 Mbps

1.25 Mbps

625 Kbps

312.5 Kbps

156.25 Kbps

Selecting Clock Frequencies Above 2.5 Mbps

To realize a 5 Mbps network, an external 40 MHz

clock must be input. However, since 40 MHz is

near the frequency of FM radio band, it is not

practical for use for noise emission reasons.

Therefore, higher frequency clocks are

generated from the 20 MHz crystal as selected

through two bits in the Setup2 register,

CKUP[1,0] as shown below. The selected clock

is supplied to the ARCNET controller.

CKUP1

CKUP0

CLOCK FREQUENCY (DATA RATE)

20 MHz (Up to 2.5Mbps) Default (Bypass)

40 MHz (Up to 5Mbps)

1 0

Reserved

1 1

Reserved

This clock multiplier is powered-down (bypassed)

on default. After changing the CKUP1 and

CKUP0 bits, the ARCNET core operation is

stopped and the internal PLL in the clock

generator is awakened and it starts to generate

the 40 MHz. The lock out time of the internal PLL

is 8uSec typically. After more than 8

sec (this

wait time is defined as 1 msec in this data sheet),

it is necessary to write command data '18H' to

the command register to re-start the ARCNET

core operation. This clock generator is called

“clock multiplier”.

Changing the CKUP1 and CKUP0 bits must be

one time or less after releasing hardware reset.

The EF bit in the SETUP2 register must be set

when the data rate is over 5 Mbps.

NETWORK RECONFIGURATION

A significant advantage of the COM20020 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 COM20020 is turned on (creating a

new active node on the network), or if the

COM20020 has not received an INVITATION TO

TRANSMIT for 420mS, or if a software reset

occurs, the COM20020 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 COM20020 senses an idle line for

greater than 41

S, which occurs only when the

token Is lost, each COM20020 starts an internal

timeout equal to 73

s times the quantity 255

minus its own ID. The COM20020 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 activity, the

COM20020 starts sending INVITATION TO

TRANSMIT with the Destination ID (DID) equal to

the currently stored NID. Within a given network,

only one COM20020 will timeout (the one with the

highest ID number). After sending the

INVITATION TO TRANSMIT, the COM20020

waits for activity on the line. If there is no activity

for 37.4

S, the COM20020 increments the NID

value and transmits another INVITATION TO

TRANSMIT using the NID equal to the DID. If

activity appears before the 37.4

S timeout

expires, the COM20020 releases control of the

line. During NETWORK RECONFIGURATION,

INVITATIONS TO TRANSMIT are sent to all NIDs

(1-255).

Each COM20020 on the network will finally have

saved a NID value equal to the ID of the

COM20020 that it released control to. At this

point, control is passed directly from one node to

the next with no wasted INVITATIONS TO

TRANSMIT being sent to ID's not on the network,

until the next NETWORK RECONFIGURATION

occurs. When a node is powered off, the previous

node attempts to pass the token to it by issuing an

INVITATION TO TRANSMIT. Since this node

does not respond, the previous node times out

and transmits another INVITATION TO

TRANSMIT to an incremented ID and eventually a

response will be received.

The NETWORK RECONFIGURATION time

depends on the number of nodes in the network,

the propagation delay between nodes, and the

highest ID number on the network, but is typically

within the range of 12 to 30.5 mS.

BROADCAST MESSAGES

Broadcasting gives a particular node the ability to

transmit a data packet to all nodes on the network

simultaneously. ID zero is reserved for this

feature and no node on the network can be

assigned ID zero. To broadcast a message, the

transmitting node's processor simply loads the

RAM buffer with the data packet and sets the DID

equal to zero. Figure 4 illustrates the position of

each byte in the packet with the DID residing at

address 0X01 or 1 Hex of the current page

selected in the "Enable Transmit from Page fnn"

command. Each individual node has the ability to

ignore broadcast messages by setting the most

significant bit of the "Enable Receive to Page fnn"

command to a logic "0".

EXTENDED TIMEOUT FUNCTION

There are three timeouts associated with the

COM20020 operation. The values of these

timeouts are controlled by bits 3 and 4 of the

Configuration Register and bit 5 of the Setup 1

Response Time

The Response Time determines the maximum

propagation delay allowed between any two

nodes, and should be chosen to be larger than

the round trip propagation delay between the two

furthest nodes on the network plus the maximum

turn around time (the time it takes a particular

COM20020 to start sending a message in

response to a received message) which is

approximately 6.4

S. The round trip propagation

delay is a function of the transmission media and

network topology. For a typical system using

RG62 coax in a baseband system, a one way

cable propagation delay of 15.5

S translates to a

distance of about 2 miles. The flow chart in Figure

1 uses a value of 37.4

S (15.5 + 15.5 + 6.4) to

determine if any node will respond.

Idle Time

The Idle Time is associated with a NETWORK

RECONFIGURATION. Figure 1 illustrates that

during a NETWORK RECONFIGURATION one

node will continually transmit INVITATIONS TO

TRANSMIT until it encounters an active node. All

other nodes on the network must distinguish

between this operation and an entirely idle line.

During NETWORK RECONFIGURATION, activity

will appear on the line every 41

S. This 41

S is

equal to the Response Time of 37.4

S plus the

time it takes the COM20020 to start retransmitting

another message (usually another INVITATION

TO TRANSMIT).

Reconfiguration Time

If any node does not receive the token within the

Reconfiguration Time, the node will initiate a

NETWORK RECONFIGURATION. The ET2 and

ET1 bits of the Configuration Register allow the

network to operate over longer distances than the

2 miles stated earlier. The logic levels on these

bits control the maximum distances over which the

COM20020 can operate by controlling the three

timeout values described above. For proper

network operation, all COM20020's connected to

the same network must have the same Response

Time, Idle Time, and Reconfiguration Time.

LINE PROTOCOL

The ARCNET line protocol is considered

isochronous because each byte is preceded by a

start interval and ended with a stop interval. Unlike

asynchronous protocols, there is a constant

amount of time separating each data byte. On a 5

Mbps network, each byte takes exactly 11 clock

intervals of 200ns each. As a result, one byte is