MAC7200 datasheet(243/976 Pages) FREESCALE

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A7S Nexus3 Programmers Model

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

165

NOTE

It is recommended to use IR[3:0] = 0x8 for “NEXUS-ACCESS”

Once the JTAG “NEXUS-ACCESS” instruction has been loaded, the JTAG port allows tool/target

communications with all Nexus registers according to the map in Table 11-21.

Reading/writing of a Nexus register then requires two (2) passes through the Data-Scan (DR) path of the

JTAG state machine (see 11.12, “IEEE 1149.1 State Machine and RD/WR Sequences”).

1. The first pass through the DR selects the Nexus register to be accessed by providing an index (see

Table 11-21), and the direction (read/write). This is achieved by loading an 8-bit value into the

JTAG Data Register (DR). This register has the following format:

0x7

HIGHZ (ARM720T)

0x8

YES

recommended for NEXUS-ACCESS

0x9

CLAMPZ (ARM720T)

0xA

YES

not publicly implemented

0xB

YES

not publicly implemented

0xC

INTEST (ARM7TDMI-S)

0xD

YES

not publicly implemented

0xE

IDCODE (ARM7TDMI-S)

0xF

BYPASS (ARM7TDMI-S)

Access: User read/write

321

NRI

R/W

Reset

000

Figure 11-23. JTAG DR for Nexus Register Access

Table 11-36. JTAG DR Field Description for Nexus Register Access

Field

Description

7–1

NRI

Nexus Register Index

Selected from values in Table 11-21

R/W

Read/Write (R/W)

0Read

1Write

Table 11-35. ARM7 JTAG Instructions (Continued)

IR[3:0]

Usable for NEXUS-ACCESS?

JTAG Instruction

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