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PDF COM20019 Data sheet ( Hoja de datos )
| Número de pieza | COM20019 | |
| Descripción | Low Cost ARCNET (ANSI 878.1) Controller | |
| Fabricantes | SMSC Corporation | |
| Logotipo |  |
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COM20019
www.DataSheet4U.com
Low Cost ARCNET (ANSI 878.1) Controller with 2K x 8
On-Board RAM
FEATURES
• New Features
- Data Rates up to 312.5 Kbps
- Programmable Reconfiguration Times
• 24 Pin DIP, 28 Pin PLCC, 48 Pin TQFP
Packages
• 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 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
GENERAL DESCRIPTION
SMSC's COM20019 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 COM20019
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
DISCONTINUED DATASHEET
1 page  
DIP PIN
NO.
1-3
4-11
23
22
19
20
21
PLCC PIN
NO.
DESCRIPTION OF PIN FUNCTIONS
NAME
SYMBOL
DESCRIPTION
MICROCONTROLLER INTERFACE
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.
4-6,8-12 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.
27 nRead/nData nRD/nDS Input. On a 68XX-like bus, nDS is an active
Strobe
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.
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 COM20019 is
accessed, enables data from the data bus to
be written to the device.
23
nReset in
nRESET
Input. This active low signal executes a
hardware reset.
24 nInterrupt nINTR
Output. This active low signal is generated by
the COM20019 when an enabled interrupt
condition occurs.
25 nChip Select nCS
Input. This active low signal selects the
COM20019 for an access.
5
DISCONTINUED DATASHEET
5 Page 
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
COM20019 to start sending a message in
response to a received message) which is
approximately 101.6 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 248 S translates
to a distance of about 32 miles. The flow chart in
Figure 1 uses a value of 597.6 S (248 + 248 +
101.6) 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 656 S. This 656
S is equal to the Response Time of 597.6 S
plus the time it takes the COM20019 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
32 miles stated earlier.
The
logic levels on these bits control the maximum
distances over which the COM20019 can operate
by controlling the three timeout values described
above. For proper network operation, all
COM20019'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
312.5 Kbps network, each byte takes exactly 11
clock intervals of 3.2 S each. As a result, one
byte is transmitted every 35.2 S and the time to
transmit a message can be precisely determined.
The line idles in a spacing (logic "0") condition. A
logic "0" is defined as no line activity and a logic
"1" is defined as a negative pulse of 1.6 S
duration. A transmission starts with an ALERT
BURST consisting of 6 unit intervals of mark (logic
"1"). Eight bit data characters are then sent, with
each character preceded by 2 unit intervals of
mark and one unit interval of space. Five types of
transmission can be performed as described
below:
Invitations To Transmit
An Invitation To Transmit is used to pass the
token from one node to another and is sent by the
following sequence:
An ALERT BURST
An EOT (End Of Transmission: ASCII code
04H)
Two (repeated) DID (Destination ID) characters
ALERT
EOT
DID
DID
BURST
11
DISCONTINUED DATASHEET
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet COM20019.PDF ] | |
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