8.4.1. Scan chain 1

This scan chain is primarily used for debugging and provides access to the core instruction and data buses.

Scan chain 1 is 67 bits long and is made up of:

These are arranged as shown in Table 8.3.

Table 8.3. Scan chain 1 bits




Data values


Control bits


Instruction values

The three control bits are:

While debugging, the value placed in the SYSSPEED control bit determines if the ARM9E-S core executes the instruction at system speed.

After the ARM946E-S has entered debug state, the first time SYSSPEED is captured and scanned out tells the debugger whether the core has entered debug state due to a breakpoint (SYSSPEED LOW) or a watchpoint (SYSSPEED HIGH). A watchpoint and a breakpoint can occur simultaneously. When a watchpoint condition occurs, the WPTANDBKPT bit must be examined by the debugger to determine whether the instruction currently in the Execute stage of the pipeline is breakpointed. If it is, WPTANDBKPT is HIGH, otherwise it is LOW.

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