JTAG Access

The JTAG Access column describes accessibility to pins, nets and busses via JTAG. Here are all the types of JTAG access:

• Read directly
• Write directly
• Read via logic
• Write via logic
• Read via NJTE
• Write via NJTE
• Grouped n pin found
• Write (AC only)
• Write (AC only from grouped n pin)

Grouped n denotes pins which are the negative side of a differential pair defined in a BSDL file. The positive (grouped p) pin is the one which can be set/read, but setting it will affect the negative pin as well, and when reading, the value which is read can depend on the value of the negative pin.

AC only write access is specified for nets (and pins) which are coupled to 1149.6 output pins through capacitors. They will be driven in Connection Test, however their value cannot be set via an XJEase SET statement.

Pin and Net Access

Any combination of the first 6 access types mentioned above are possible. Grouped n access is only reported if no other access is present. Here are some example combinations the way they are expressed in the column, and a description of what they mean:

• None = No access via JTAG
• Read = Read directly
• Read / Write = Read directly and write directly
• Read / Write (Logic) = Read directly and write via logic
• Write (Direct+Logic) = Write directly and write via logic
• Read / Write (Direct+Logic) = Read directly and write directly and write via logic
• Grouped n pin found = Net's value is affected by SET statements on another pin, and/or value on net can affect values read from another pin
• Read (NJTE) / Write = Read via NJTE

Notice in the example Read / Write (Direct+Logic) it does not include read via logic.

Bus access

If all pins in a bus have identical access, then that access will be displayed. However if there are various types of access, two new descriptions can be used:

• Partial = Combination of one type of access and no access
• Mixed = Two or more different types of access