10 Mbps ARCNET (ANSI 878.1) Controller with 2Kx8 On-Board RAM
Datasheet
Table 6.12 - Setup 1 Register
BIT
BIT NAME
SYMBOL
DESCRIPTION
7
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.
6
Four NACKS
FOUR
NACKS
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 COM20022I 3V. This
bit, when reset, will set the EXNACK bit after 128 NACKs
to Free Buffer Enquiry. The default is 128.
5
4
Reserved
Do not set.
Receive All
RCVALL
This bit, when set, allows the COM20022I 3V 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 COM20022I 3V's programmed
node ID. This feature can be used to put the COM20022I
3V in a 'listen-only' mode, where the transmitter is
disabled and the COM20022I 3V is not passing tokens.
Defaults low.
3,2,1 Clock Prescaler
Bits 3,2,1
CKP3,2,1
These bits are used to determine the data rate of the
COM20022I 3V. The following table is for a 20 MHz
crystal: (Clock Multiplier is bypassed)
CKP3 CKP2 CKP1 DIVISOR
SPEED
2.5Mbs
0
0
0
0
1
0
0
1
1
0
0
1
0
1
0
8
16
32
64
128
1.25Mbs
625Kbs
312.5Kbs
156.25Kbs
Note: The lowest data rate achievable by the COM20022I
3V is 156.25Kbs. Defaults to 000 or 2.5Mbs. For
Clock Multiplier output clock speed greater than 20
MHz, CKP3, CKP2 and CKP1 must all be zero.
0
Slow Arbitration
Select
SLOWARB This bit, when set, will divide the arbitration clock by 2.
Memory cycle times will increase when slow arbitration is
selected.
Note: For clock multiplier output clock speeds greater
than 40 MHz, SLOWARB must be set. Defaults to
low.
Revision 02-27-06
Page 42
SMSC COM20022I 3V
DATASHEET
SMSC [ SMSC CORPORATION ]
