COM20020-5 Datasheet, PDF (27/58 Pages) SMSC Corporation – Universal Local Area Network Controller with 2K x 8 On-Board RAM

BIT
BIT NAME
7 Reset
6 Command
Chaining Enable
5 Transmit Enable
4,3 Extended
Timeout 1,2
2 Backplane
1,0 Sub Address 1,0
TABLE 8 - CONFIGURATION REGISTER
SYMBOL
DESCRIPTION
RESET
A software reset of the COM20020-5 is executed by writing a logic "1"
to this bit. A software reset does not reset the microcontroller
interface mode, nor does it affect the Configuration Register. The
only registers that the software reset affect are the Status Register,
the Interrupt Mask Register, and the Diagnostic Status Register. This
bit must be brought back to logic "0" to release the reset.
CCHEN
This bit, if high, enables the Command Chaining operation of the
device. Please refer to the Command Chaining section for further
details. A low level on this bit ensures software compatibility with
previous SMSC ARCNET devices.
TXEN
When low, this bit disables transmissions by keeping nPULSE1,
nPULSE2 if in non-Backplane Mode, and nTXENABLE inactive.
When high, it enables the above signals to be activated during
transmissions. This bit defaults low upon reset. This bit is typically
enabled once the Node ID is determined, and never disabled during
normal operation. Please refer to the Improved Diagnostics section
for details on evaluating network activity.
ET1, ET2
These bits allow the network to operate over longer distances than the
default maximum 2 miles by controlling the Response, Idle, and
Reconfiguration Times. All nodes should be configured with the
same timeout values for proper network operation. For the
COM20020-5 with a 40 MHz crystal the bit combinations follow:
Response IdleTime Reconfig
ET2
ET1
Time ( S)
( S)
Time (mS)
0
0
596.8
656
840
0
1
298.4
328
840
1
0
74.7
82
840
1
1
37.35
41
420
BACK-
PLANE
A logic "1" on this bit puts the device into Backplane Mode signalling
which is used for Open Drain and Differential Driver interfaces.
SUBAD 1,0 These bits determine which register at address 07 may be accessed.
The combinations are as follows:
SUBAD1 SUBAD0Register
0
0Tentative ID
0
1Node ID
1
0Setup
1
1Next ID
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