5Mbps ARCNET (ANSI 878.1) Controller with 2K x 8 On-Chip RAM
BIT
BIT NAME
Command
SYMBOL
DESCRIPTION
6
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.
Chaining Enable
5
Transmit Enable
TXEN
When low, this bit disables transmissions by keeping
nPULSE1, nPULSE2 if in non-Backplane Mode, and nTXEN
pin 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.
4,3 Extended
Timeout 1,2
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 COM20020I with a 20 MHz
crystal oscillator, the bit combinations follow:
Reconfig
Response Idle Time
Time
(mS)
840
840
840
ET2
0
0
1
1
ET1
0
1
0
1
Time (μS)
596.6
(μS)
656
328
164
41
298.4
149.2
420
37.4
Note: These values are for 5Mbps and RCNTMR[1,0]=00.
Reconfiguration time is changed by the RCNTMR1 and
RCNTMR0 bits.
2
Backplane
BACK-
PLANE
A logic "1" on this bit puts the device into Backplane Mode
signaling which is used for Open Drain and Differential Driver
interfaces.
1,0 Sub Address 1,0
SUBAD
1,0
These bits determine which register at address 07 may be
accessed. The combinations are as follows:
SUBAD1 SUBAD0 Register
0
0
1
1
0
1
0
1
Tentative ID
Node ID
Setup 1
Next ID
See also the Sub Address Register.
Revision 12-06-06
32
SMSC COM20020I 3.3V
DATASHEET
SMSC [ SMSC CORPORATION ]
