Datasheet

4–15
Table 4–9. PHY-Configuration Functions
FIELD NAME DESCRIPTION
root_ID The root_ID field is the physical_ID of the node to have its force_root bit set (only meaningful when
R is set).
R When R is set, the force-root bit of the node identified in root_ID is set and the force_root bit of all
other nodes are cleared. When R is cleared, root_ID is ignored.
T When T is set, the gap count field of all the nodes is set to the value in the gap_cnt field.
gap_cnt The gap_cnt field contains the new value for gap count for all nodes. This value goes into effect
immediately upon receipt and remains valid after the next bus reset. After the second reset, gap_cnt
is set to 63h unless a new PHY-configuration packet is received.
4.8 Link-On Transmit
The transmit format of the link-on packet is shown in Figure 4–22 and described in Table 4–10. The link-on
packet contains three quadlets, which are loaded into the ATF. The first quadlet is the tCode for an
unformatted packet. This is written into ATF_First at address 80h and has a value of 0000_00E0h. The
second quadlet consists of actual data. This is written into the ATF_Continue at address 84h and has a value
of the first quadlet of the link-on packet. The third quadlet is the logical inverse of the second quadlet and
it written into the ATF_Continue&Update at address 8Ch and has a value of the second quadlet of the link-on
packet.
There is a possibility of a false header error on receipt of a link-on packet. If the first 16 bits of a link-on packet
happen to match the destination identifier of a node (bus number and node number), the TSB12LV01B on
that node issues a header error since the node misinterprets the link-on packet as a data packet addressed
to the node. The suggested solution to this potential problem is to assign bus numbers that all have the most
significant bit set to 1. Since the all-ones case is reserved for addressing the local bus, this leaves only 511
available unique bus identifiers. This is an artifact of the IEEE 1394-1995 standard.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
logical inverse of first 16 bits of first quadlet
PHY_ID
01 0000000000000000
1111111111111111
00000000
11100000000000000000000000000000
Packet
Identifier
tcode=E
Figure 4–22. Link-On Packet Format
Table 4–10. Link-On Packet Functions
FIELD NAME DESCRIPTION
PHY_ID This field is the physical_ID of the node this packet is addressed to.