5Mbps ARCNET (ANSI 878.1) Controller with 2K x 8 On-Chip RAM
Datasheet
Table 6.10 - Setup 1 Register
SYMBOL
P1MODE
BIT
BIT NAME
Pulse1 Mode
DESCRIPTION
7
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 COM20020ID. 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 COM20020ID 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 COM20020ID's
programmed node ID. This feature can be used to put the
COM20020ID in a 'listen-only' mode, where the transmitter is
disabled and the COM20020ID is not passing tokens. Defaults
low.
3,2,1 Clock Prescaler Bits
CKP3,2,1
These bits are used to determine the data rate of the
COM20020ID. The following table is for a 20 MHz crystal: (Clock
Multiplier is bypassed)
3,2,1
CKP3
CKP2 CKP1 DIVISOR
SPEED
0
0
0
0
1
0
0
1
1
0
0
1
0
1
0
8
2.5Mbs
16
32
64
128
1.25Mbs
625Kbs
312.5Kbs
156.25Kbs
NOTE: The lowest data rate achievable by the COM20020ID 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 12-05-06
Page 36
SMSC COM20020I Rev D
DATASHEET
SMSC [ SMSC CORPORATION ]
