|
| Table 6 - Command Register | |
DATA | COMMAND |
| DESCRIPTION |
|
|
|
|
0000 0000 | Clear |
| This command is used only in the Command Chaining operation. Please |
| Transmit |
| refer to the Command Chaining section for definition of this command. |
| Interrupt |
|
|
|
|
|
|
0000 0001 | Disable |
| This command will cancel any pending transmit command (transmission |
| Transmitter |
| that has not yet started) and will set the TA (Transmitter Available) status |
|
|
| bit to logic "1" when the COM20020 next receives the token. |
|
|
|
|
0000 0010 | Disable |
| This command will cancel any pending receive command. If the |
| Receiver |
| COM20020 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 |
| This command allows the COM20020 to receive data packets into RAM |
| Receive to |
| buffer page fnn and resets the RI status bit to logic "0". The values placed |
| Page fnn |
| 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. |
|
|
|
|
00fn n011 | Enable |
| This command prepares the COM20020 to begin a transmit sequence |
| Transmit from |
| from RAM buffer page fnn the next time it receives the token. The values |
| Page fnn |
| 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 1 for |
|
|
| details of the transmit sequence and its relation to the TA and TMA status |
|
|
| bits. |
|
|
|
|
0000 c101 | Define |
| This command defines the maximum length of packets that may be |
| Configuration |
| 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 COM20020. 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 |
| This command is used only in the Command Chaining operation. Please |
| Receive |
| refer to the Command Chaining section for definition of this command. |
| Interrupt |
|
|
|
|
|
|
27
