10 Mbps ARCNET (ANSI 878.1) Controller with 2Kx8 On-Chip RAM
Datasheet
Table 6.10 - Setup 1 Register
SYMBOL DESCRIPTION
BIT
BIT NAME
Pulse1 Mode
7
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. 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 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's
programmed node ID. This feature can be used to put the
COM20022I in a 'listen-only' mode, where the transmitter is
disabled and the COM20022I 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.
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 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.
SMSC COM20022I
Page 43
Revision 09-27-07
DATASHEET
SMSC [ SMSC CORPORATION ]
