VSC7440 datasheet(309/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

292

Figure 89 •

READ Command

Figure 90 •

WRITE Command

3.30.5

VRAP READ-MODIFY-WRITE Command

The READ-MODIFY-WRITE command does read/modify/write-back on any 32-bit register inside the

device.

The READ-MODIFY-WRITE command is 12 bytes wide and consists of one 32-bit address field, which is

32-bit aligned. The two least significant bits of the address set to 11 followed by one 32-bit write-data field

followed by one 32-bit overwrite-mask field. For bits set in the overwrite mask, the corresponding bits in

the write data field are written to the register while bits cleared in the overwrite mask are untouched when

writing to the register. The following illustration shows the command.

Figure 91 •

READ-MODIFY-WRITE Command

3.30.6

VRAP IDLE Command

The IDLE command does not access registers in the device. Instead it just copies itself (the entire

command) into the VRAP response. This can be used for padding to fulfill the minimum transmission unit

size, or an external CPU can use it to insert a unique code into each VRAP request frame so that it can

separate different replies from each other.

The IDLE command is 4 bytes wide and consists of one 32-bit code word with the four least significant

bits of the code word set to 0000. The following illustration depicts the request command and the

associated response.

Figure 92 •

IDLE Command

3.30.7

VRAP PAUSE Command

The PAUSE command does not access registers in the device. Instead it causes the VRAP engine to

enter a wait state and remain there until the pause time has expired. This can be used to ensure

sufficient delay between VRAP commands when this is needed.

The PAUSE command is 4 bytes wide and consists of one 32-bit code word with the four least significant

bits of the code word set to 0100. The wait time is controlled by the 28 most significant bits of the wait

command. The time unit is 1 us. The following illustration depicts the PAUSE command.

Request:

32 bits

Response:

32 bits

Request:

32 bits

Request:

Overwrite mask

32 bits

Any 28-bit value

Request:

32 bits

Copy of value

Response:

0000

32 bits

0000

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