
21145
12
Preliminary 
Datasheet
sr_di
O
137
113
Serial ROM data-in signal. This pin serially shifts the write 
data from the 21145 to the serial ROM device. 
sr_do
I
136
112
Serial ROM data-out signal. This pin serially shifts the 
read data from the serial ROM device to the 21145. 
stop_l
I/O
71
56
Stop indicator indicates that the current target is 
requesting the bus master to stop the current transaction.
The 21145 responds to the assertion of stop_l when it is 
the bus master, either to disconnect, retry, or abort.
tp_rd–
I
10
10
Twisted-pair negative differential receive data from the 
twisted-pair lines.
tp_rd+
I
9
9
Twisted-pair positive differential receive data from the 
twisted-pair lines.
tp_td–
tp_td– –
O
O
5
4
5
4
Twisted-pair negative differential transmit data. The 
positive and negative differential transmit data outputs 
are combined resistively outside the 21145 with 
equalization to compensate for intersymbol interference 
on the twisted-pair medium.
tp_td+
tp_td+ +
O
O
6
7
6
7
Twisted-pair positive differential transmit data. The 
positive and negative differential transmit data outputs 
are combined resistively outside the 21145 with 
equalization to compensate for intersymbol interference 
on the twisted-pair medium.
trdy_l
I/O
61
52
Target ready indicates the target agent’s ability to 
complete the current data phase of the transaction.
A data phase is completed on any clock when both trdy_l 
and irdy_l are asserted.  Wait cycles are inserted until 
both irdy_l and trdy_l are asserted together.
When the 21145 is the bus master, target ready is 
asserted by the bus slave on the read operation, which 
indicates that valid data is present on the ad lines. During 
a write cycle, it indicates that the target is prepared to 
accept data.
vcap_h
I
134
110
Capacitor input for analog phase-locked loop logic.
vdd
P
1, 2, 8, 25, 
26, 34, 44, 
45, 54, 67, 
68, 83, 88, 
89, 95, 113, 
130, 131, 
157, 168, 
173
1, 2, 8, 18, 
26, 36, 37, 
46, 54, 67, 
72, 73, 79, 
95, 107, 125, 
136, 141
3.3-V supply input. These pins should be connected to 
the auxiliary power, if such power exists. Otherwise, these 
pins should be connected to the main power. 
vddac
P
133, 135
109,111
Supplies +3.3-V input for analog phase-locked loop logic. 
These pins should each be decoupled with a separate 0.1 
μf capacitor to ground. The capacitors should be located 
as close to the package pins as possible.
vdd_clamp
P
28
20
Supplies +5-V or +3.3-V reference for clamp logic. This 
pin is also used to determine the lack of main power when 
the auxiliary power is on. It should be connected to the 
main power.
This pin determines whether 5 V or 3.3 V signalling is 
used on the PCI bus.
Table 1. Functional Description of 21145 Signals (Sheet 7 of 8)
Signal
Type
Pin 
Number, 
176-pin
Pin 
Number, 
144-pin
Description