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5.4
Scan chains and JTAG interface
ARM DDI0145B
There are three scan chains inside the ARM9TDMI. These allow testing, debugging and
programming of the EmbeddedICE macrocell watchpoint units. The scan chains are
controlled by a JTAG-style Test Access Port (TAP) controller. In addition, support is
provided for an optional fourth scan chain. This is intended to be used for an external
boundary scan chain around the pads of a packaged device. The signals provided for this
scan chain are described on Scan chain 3 on page 5-25.
The three scan chains of the ARM9TDMI are referred to as scan chain 0, 1 and 2.
Note
The ARM9TDMI TAP controller supports 32 scan chains. Scan chains 0 to 15 have
been reserved for use by ARM. Any extension scan chains should be implemented in
the remaining space. The SCREG[4:0] signals indicate which scan chain is being
accessed.
Copyright © 1998, 1999 ARM Limited. All rights reserved.
Debug Support
5-11
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