Intel III Xeon 800 MHz 80526KZ800256 User Manual
Product codes
80526KZ800256
INTEGRATION TOOLS
81
The TDO signal of each processor has a 2.5V Tolerant open-drain driver. The TDI signal of each
processor contains a 150
processor contains a 150
Ω pull-up to Vcc
TAP
. When connecting one processor to the next, or connecting to
the TDI of the first processor, no external pull-up is required. However, the last processor of the chain
does require a pull-up before passing the signal to the next device in the chain.
does require a pull-up before passing the signal to the next device in the chain.
8.1.6.4 Signal Note: TCK and TMS
WARNING
A significant number of target systems have had signal integrity issues with the TCK signal. TCK
is a critical clock signal and must be routed accordingly; make sure to observe power and ground
plane integrity for this signal. Follow the guidelines below and assure the quality of the signal
when beginning use of an ITP to debug your target.
is a critical clock signal and must be routed accordingly; make sure to observe power and ground
plane integrity for this signal. Follow the guidelines below and assure the quality of the signal
when beginning use of an ITP to debug your target.
Due to the number of loads on the TCK signal, special care should be taken when routing this. Poor routing
can lead to multiple clocking of some agents on the debug chain, usually on the falling edge of TCK. This
causes information to be lost through the chain and can result in bad commands being issued to some agents
on the chain. Systems using other TCK routing schemes, particularly those with ‘T' or ‘Y' configurations where
the trace from the source to the ‘T' is long, could have signal integrity problems.
The suggested routing scheme is to drive each of the agent TCK signals individually from a buffer device.
Figure 31 shows how the TCK signal should be routed to the agents in a 4-way Pentium® III Xeon™
processor-based system incorporating the Intel® 450NX PCIset. A Bessel filter is recommended over a series
termination at the output of each buffer. The values shown in Figure 31 are only examples. The designer
should determine the LC values appropriate for their particular application.
If it is desired to ship production systems without the 2.5V buffers installed, then pull-up resistors
should be placed at the outputs to prevent TCK from floating.
Debug
Port
SC330.1
0
SC330.1
1
SC330.1
2
SC330.1
3
To each device, other
JTAG
...
TCK
2.5V
Buffers
74LVQ244
Type
Pull up
Resistor
2.5V
56
pF
pF
56
pF
pF
56
pF
pF
56
pF
pF
56
pF
pF
56
pF
pF
100
nH
100
nH
100
nH
100
nH
100
nH
100
nH
Figure 31. TCK with individual buffering scheme
The ITP buffer board drives the TCK signal through the debug port, to the buffered device(s).