5Mbps ARCNET (ANSI 878.1) Controller with 2K x 8 On-Chip RAM
Datasheet
Table 6.5 - Command Register
DESCRIPTION
DATA
COMMAND
Clear
0000 0000
This command is used only in the Command Chaining operation. Please
refer to the Command Chaining section for definition of this command.
Transmit
Interrupt
Disable
0000 0001
0000 0010
This command will cancel any pending transmit command (transmission
that has not yet started) and will set the TA (Transmitter Available) status
bit to logic "1" when the COM20020ID next receives the token.
Transmitter
Disable
This command will cancel any pending receive command. If the
COM20020ID is not yet receiving a packet, the RI (Receiver Inhibited) bit
will be set to logic "1" the next time the token is received. If packet
reception is already underway, reception will run to its normal
conclusion.
Receiver
b0fn n100
Enable
This command allows the COM20020ID to receive data packets into
RAM buffer page fnn and resets the RI status bit to logic "0". The values
placed in the "nn" bits indicate the page that the data will be received
into (page 0, 1, 2, or 3). If the value of "f" is a logic "1", an offset of 256
bytes will be added to that page specified in "nn", allowing a finer
resolution of the buffer. Refer to the Selecting RAM Page Size section
for further detail. If the value of "b" is logic "1", the device will also
receive broadcasts (transmissions to ID zero). The RI status bit is set to
logic "1" upon successful reception of a message.
Receive to
Page fnn
00fn n011
Enable
Transmit from
Page fnn
This command prepares the COM20020ID to begin a transmit sequence
from RAM buffer page fnn the next time it receives the token. The
values of the "nn" bits indicate which page to transmit from (0, 1, 2, or 3).
If "f" is logic "1", an offset of 256 bytes is the start of the page specified in
"nn", allowing a finer resolution of the buffer. Refer to the Selecting RAM
Page Size section for further detail. When this command is loaded, the
TA and TMA bits are reset to logic "0". The TA bit is set to logic "1" upon
completion of the transmit sequence. The TMA bit will have been set by
this time if the device has received an ACK from the destination node.
The ACK is strictly hardware level, sent by the receiving node before its
microcontroller is even aware of message reception. Refer to Figure 3.1
for details of the transmit sequence and its relation to the TA and TMA
status bits.
0000 c101
Define
Configuration
This command defines the maximum length of packets that may be
handled by the device. If "c" is a logic "1", the device handles both long
and short packets. If "c" is a logic "0", the device handles only short
packets.
000r p110
0000 1000
Clear Flags
This command resets certain status bits of the COM20020ID. A logic "1"
on "p" resets the POR status bit and the EXCNAK Diagnostic status bit.
A logic "1" on "r" resets the RECON status bit.
Clear
This command is used only in the Command Chaining operation. Please
refer to the Command Chaining section for definition of this command.
Receive
Interrupt
0001 1000
Start Internal
Operation
This command restarts the stopped internal operation after changing
CKUP1 or CKUP0 bit.
SMSC COM20020I Rev D
Page 33
Revision 12-05-06
DATASHEET
SMSC [ SMSC CORPORATION ]
