3.4. TAP interface wiring

Both the ARM7 microprocessor and the ETM7 provide scan chain expansion inputs. These are:

In each case this input is routed through to TDO when an unimplemented scan chain is selected. This allows the ARM7 and ETM7 TAP controllers to run in parallel, with a single TDO output. The ARM recommended connectivity is shown in Figure 3.6.

Figure 3.6. ARM7TDMI and ETM7 TAP interface structure

The ARM7TDMI-S does not provide a scan chain expansion input. ARM recommends the connectivity shown in Figure 3.7 to allow the ARM7TDMI-S and ETM7 TAP controllers to run in parallel, with a single TDO output.

Figure 3.7. ARM7TDMI-S and ETM7 TAP interface structure

Note

For clarity, nTRST is omitted from figures relating to the TAP interface. You must connect nTRST to all TAPs on the chip. See the Multi-ICE User Guide for details.

If you are using an ARM7TDMI core, and your ASIC includes another scan chain controlled by the ARM TAP controller, then the TDO of this scan chain can be connected into the otherwise unused ARMTDO input on the ETM7. This is shown in Figure 3.8.

Figure 3.8. Using ETM7 and ARM7TDMI with an external scan chain

If you are using an ARM7TDMI-S, then you require an external mux for selecting the scan chain connected to the ETM7 ARMTDO input.

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