Datasheet

TSB81BA3D, TSB81BA3DI
IEEE 1394b THREE-PORT CABLE TRANSCEIVER/ARBITER
SLLS559E − DECEMBER 2002 − REVISED JUNE 2006
30
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
PRINCIPLES OF OPERATION (1394a−2000 INTERFACE)
LLC service request (continued)
The length of the stream varies depending on the type of request as shown in Table 12.
Table 12. Request Stream Bit Length
REQUEST TYPE NUMBER OF BITS
Bus request 7 or 8
Read register request 9
Write register request 17
Acceleration control request 6
Regardless of the type of request, a start bit of 1 is required at the beginning of the stream, and a stop bit of 0
is required at the end of the stream. The second through fourth bits of the request stream indicate the type of
the request. In the descriptions below, bit 0 is the most significant and is transmitted first in the request bit stream.
The LREQ terminal is normally low.
Table 13 shows the encoding for the request type.
Table 13. Request Type Encoding
LR1−LR3 NAME DESCRIPTION
000 ImmReq Immediate bus request. Upon detection of idle, the PHY takes control of the bus immediately without arbitration.
001 IsoReq Isochronous bus request. Upon detection of idle, the PHY arbitrates for the bus without waiting for a subaction gap.
010 PriReq Priority bus request. The PHY arbitrates for the bus after a subaction gap, ignores the fair protocol.
011 FairReq Fair bus request. The PHY arbitrates for the bus after a subaction gap, follows the fair protocol.
100 RdReg The PHY returns the specified register contents through a status transfer
101 WrReg Write to the specified register
110 AccelCtl Enable or disable asynchronous arbitration acceleration
111 Reserved Reserved
For a bus request, the length of the LREQ bit stream is 7 or 8 bits as shown in Table 14.
Table 14. Bus Request
BIT(s) NAME DESCRIPTION
0 Start bit Indicates the beginning of the transfer (always 1)
1−3 Request type Indicates the type of bus request. See Table 13.
4−6 Request speed Indicates the speed at which the PHY sends the data for this request. See Table 15 for the encoding of this field.
7 Stop bit Indicates the end of the transfer (always 0). If bit 6 is 0, then this bit may be omitted.
Table 15 shows the 3-bit request speed field used in bus requests.
Table 15. Bus Request Speed Encoding
LR4−LR6 DATA RATE
000 S100
010 S200
100 S400
All Others Invalid