Actel Silicon Explorer II User Manual page 26

Appendix A: Debugging SX/SX-A/eX Devices Using Silicon Explorer II
Probe Pins
Design
Considerations
20
Table 1 enumerates all the possible configuration of the diagnostic
pins.
Table 1. Diagnostic Pin Configuration
Dedicated JTAG Mode
•
TCK, TDI, and TDO are dedi-
cated diagnostic pins.
When you select the "Reserve Probe Pin" box, you direct the layout
tool to reserve the PRA and PRB pins as diagnostic pins. This option is
merely a guideline. If the Layout tool requires that the PRA and PRB
pins be user I/O's to achieve successful layout, then the tool will use
these pins as user I/Os. If you assign user I/Os to the PRA and PRB
pins and select the "Reserve Probe Pin" option, the Layout tool will
override the "Reserve Probe Pin" option.
Avoid using the TDI, TCK, TDO, PRA, and PRB pins as input or
bidirectional ports. Since these pins are active during probing, critical
input signals through these pins are not available. In addition, do not
program the Security Fuse. Programming the Security Fuse disables the
Probe Circuit.
Flexible JTAG Mode
•
Use TCK, TDI and TDO as I/Os.
•
You need the 10K pull-up resistor
on the TMS Pin.