COM20051I Datasheet, PDF (33/74 Pages) SMSC Corporation – Integrated Microcontroller and ARCNET (ANSI 878.1) Interface

BIT
7
6
5
4
3,2,1
Table 13 - Setup Register
BIT NAME
SYMBOL
DESCRIPTION
Pulse1 Mode P1MODE
This bit determines the type of PULSE1 output driver
used in Backplane Mode. When high, a push/pull output
is used. When low, an open drain output is used. The
default is open drain.
Four NACKS FOUR NACKS
Reserve
Reserve
Receive All RCVALL
Clock
CKP2,1,0
Prescaler Bits
3,2,1
This bit, when set, will cause the EXNACK bit in the
Diagnostic Status Register to set after four NACKs to
Free Buffer Enquiry are detected by the ARCNET core.
This bit, when reset, will set the EXNACK bit after 128
NACKs to Free Buffer Enquiry. The default is 128.
This bit, when set, scales down protocol timeout values
of Response Time and Idle Time but not Reconfiguration
Time to optimize network performance in short
topologies. Provides a scaling factor of ÷ 3. Defaults to
a zero. Must be reset to be ARCNET compliant.
This bit, when set, allows the COM20051I to receive all
valid data packets on the network, regardless of their
destination ID. This mode can be used to implement a
network monitor with the transmitter on- or off-line. Note
that ACKs are only sent for packets received with a
destination ID equal to the COM20051I's programmed
node ID. This feature can be used to put the
COM20051I in a 'listen-only' mode, where the transmitter
is disabled and the COM20051I is not passing tokens.
Defaults low.
These bits are used to determine the data rate of the
COM20051I. The following table is for a 40MHz crystal:
Response
CKP3 CKP2 CKP1 DIVISOR
CLOCK
0
00
8
2.5 Mbps
0
01
16
1.25 Mbps
0
10
32
625 Kbps
0
11
64
312.5 Kbps
1
00
128 156.25 Kbps
1
01
256
Reserved
1
10
Reserved
1
11
Reserved
0
Slow
SLW-ARB
Arbitration
Select
NOTE: The lowest data rate achievable by the
COM20051I is 156.25 Kbps. A divide by 256 is provided
for those systems that use faster clock speeds. Defaults
to 000 or 2.5 Mbps.
This bit, when set, will divide the arbitration clock by 2.
Memory cycle times will increase when slow arbitration
is selected.
Note: For 5 Mbps operation, SLOWARB must be set.
Defaults to low.
SMSC DS – COM20051I
Page 33
Rev. 03/27/2000