Epson ARM720T User Manual

Purpose

Changes the current TAP instruction.

Length

4 bits.

Operating mode

In the SHIFT-IR state, the instruction register is selected as the 

serial path between DBGTDI, and DBGTDO.
During the CAPTURE-IR state, the binary value 0001 is loaded 

into this register. This value is shifted out during SHIFT-IR (least 

significant bit first), while a new instruction is shifted in (least 

significant bit first).
During the UPDATE-IR state, the value in the instruction register 

becomes the current instruction. 
On reset, IDCODE becomes the current instruction.
There is no parity bit.

Purpose

Changes the current active scan chain.

Length 4 

bits.

Operating mode

 SCAN_N as the current instruction in the SHIFT-DR state selects 

the scan path select register as the serial path between DBGTDI, 

and DBGTDO.
During the CAPTURE-DR state, the value b1000 binary is loaded 

into this register. This value is loaded out during SHIFT-DR (least 

significant bit first), while a new value is loaded in (least 

significant bit first). During the UPDATE-DR state, the value in 

the register selects a scan chain to become the currently active scan 

chain. All additional instructions, such as INTEST, then apply to 

that scan chain.
The currently-selected scan chain changes only when a SCAN_N 

instruction is executed, or when a reset occurs. On reset, scan chain 

0 is selected as the active scan chain.

Table 9-5 shows the scan chain number allocation.

Table 9-5  Scan chain number allocation

0

(User-implemented)

1

Debug

2

EmbeddedICE-RT 
programming

3

Reserved

a

a.

When selected, reserved scan 

chains scan out zeros.

4

Reserved

a

8

Reserved

a