32
32
Table 9 - Command Register
DATA
COMMAND
DESCRIPTION
0000 0000
Clear
Transmit
Interrupt
This command is used only in the Command Chaining operation.
Please refer to the Command Chaining section for definition of this
command.
0000 0001
Disable
Transmitter
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 ARCNET core next receives the token.
0000 0010
Disable
Receiver
This command will cancel any pending receive command. If the
COM20051 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.
b0fn n100
Enable
Receive to
Page fnn
This command allows the ARCNET core 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 00 or 01). 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.
00fn n011
Enable
Transmit from
Page fnn
This command prepares the ARCNET core 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 or 1).
If "f" is logic "1", an offset of 256 bytes is 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. 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 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
Clear Flags
This command resets certain status bits of the COM20051. 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.
0000 1000
Clear
Receive
Interrupt
This command is used only in the Command Chaining operation.
Please refer to the Command Chaining section for definition of this
command.
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