
52
5.1.1
Quadlet Transmit
The quadlet-transmit format is shown in Figure 51 and Figure 52, and is described in Table 53. The first
quadlet contains packet information. The second and third quadlets contain the 64-bit, quadlet-aligned
address. The fourth quadlet is data used only for write requests and read responses. For read requests and
write responses, the quadlet data field is omitted.
spd
30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
31
quadlet Data
destination Offset Low
destination Offset High
destination ID
Priority
tCode
rt
tLabel
Figure 51. Quadlet Transmit Format (Write Request)
spd
30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
31
quadlet data
rCode
destination ID
Priority
tCode
rt
tLabel
Figure 52. Quadlet Transmit Format (Read Response)
Table 53. Quadlet Transmit Format Functions
FIELD NAME
DESCRIPTION
spd
The spd field indicates the speed at which the current packet is to be sent. 00 = 100 Mb/s,
01 = 200 Mb/s, and 10 = 400 Mb/s. For this implementation, 11 is undefined.
tLabel
The tLabel field is the transaction label, which is a unique tag for each outstanding transaction
between two nodes. This field is used to pair up a response packet with its corresponding
request packet.
rt
The rt field is the retry code for the current packet: 00 = new, 01 = retry_X, 10 = retry_A, and
11 = retry_B.
tCode
The tCode field is the transaction code for the current packet (see Table 610 of IEEE–1394
standard).
priority
The priority field contains the priority level for the current packet. For cable implementation,
the value of the bits must be zero (for backplane implementation, see clauses 5.4.1.3 and
5.4.2.1 of the IEEE-1394 standard).
destinationID
The destinationID field is the concatenation of the 10-bit bus number and the 6-bit node
number that forms the destination node address of the current packet.
destination OffsetHigh,
destination OffsetLow
The concatenation of these two fields addresses a quadlet in the destination node address
space. This address must be quadlet aligned (modulo 4).
quadlet data
For write requests and read responses, the quadlet data field holds the data to be transferred.
For write responses and read requests, this field is not used and should not be written into the
FIFO.