Datasheet

TSB81BA3D, TSB81BA3DI

IEEE 1394b THREE-PORT CABLE TRANSCEIVER/ARBITER

SLLS559E − DECEMBER 2002 − REVISED JUNE 2006

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION (1394B INTERFACE)

LLC service request (continued)

Table 30. Write Register Request

BIT(s) NAME DESCRIPTION

0 Start bit Indicates the beginning of the transfer (always 1)

1−4 Request type A 1011 indicates this is a write register request

5−8 Address Identifies the address of the PHY register to be written

9−16 Data Gives the data that is to be written to the specified register address

17 Stop bit Indicates the end of the transfer (always 0)

For a link notification request, the length of the LREQ bit stream is 6 bits as shown in Table 31.

Table 31. Link Notification Request

BIT(s) NAME DESCRIPTION

0 Start bit Indicates the beginning of the transfer (always 1)

1−4 Request type A 1100, 1101, or 1110 indicates this is a link notification request

5 Stop bit Indicates the end of the transfer (always 0)

For fair or priority access, the LLC sends a bus request at least one clock after the PHY-LLC interface becomes

idle. The PHY queues all bus requests and can queue one request of each type. If the LLC issues a different

request of the same type, then the new request overwrites any nonserviced request of that type. Note, upon

the receipt (CTL terminals are asserted to the receive state, 10b) of a packet, queued requests are not cleared

by the PHY.

The cycle master node uses a cycle start request (Cyc_Start_Req) to send a cycle start message. After

receiving or transmitting a cycle start message, the LLC can issue an isochronous bus request (IsoReq). The

PHY clears an isochronous request only when the serial bus has been won.

To send an acknowledge packet, the LLC must issue an immediate bus request (Immed_Req) during the

reception of the packet addressed to it. This is required in order to minimize the idle gap between the end of

the received packet and the start of the transmitted acknowledge packet. As soon as the received packet ends,

the PHY immediately grants control of the bus to the LLC. The LLC sends an acknowledgment to the sender

unless the header CRC of the received packet is corrupted. In this case, the LLC does not transmit an

acknowledge, but instead cancels the transmit operation and releases the interface immediately; the LLC must

not use this grant to send another type of packet. After the interface is released the LLC may proceed with

another request.

For write register requests, the PHY loads the specified data into the addressed register as soon as the request

transfer is complete. For read register requests, the PHY returns the contents of the addressed register to the

LLC at the next opportunity through a PHY status transfer. A write or read register request may be made at any

time, including while a bus request is pending. Once a read register request is made, the PHY ignores further

read register requests until the register contents are successfully transferred to the LLC. A bus reset does not

clear a pending read register request.