MAC7200 datasheet(170/976 Pages) FREESCALE

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Debug Implementation

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

•

TDI - Serial Data In

•

TDO - Serial Data Out

Through the JTAG interface, the following may be accessed (See also Table 11-8):

•

ARM7 EICE registers

•

Nexus registers

•

Debug register (SC4)

Although there are several blocks of logic that can be accessed through the JTAG interface, the MAC72xx

contains only a single TAP state machine, located in the ARM7 complex. This TAP State Machine is used

to select the various JTAG-accessible registers in the system. This is illustrated in Figure 8-1.

Figure 8-1. JTAG Interface Overview

Selection between the different pieces of Test Logic on the MAC72xx is done by decoding the dbg_ir[3:0]

and dbg_scan_n[3:0] signals from the TAP state machine. Table 8-1 shows the decoding for the

MAC72xx. The dbg_tapsm[3:0] signal is the current state of the TAP state machine, and is used by the

PTI and Nexus to determine which JTAG state the TAP is currently in.

Based on which test logic is selected, the TCK, TMS, TDI and TDO inputs/outputs are routed to the correct

destination. The following figures illustrate this.

Table 8-1. JTAG Test Logic Selection

dbg_ir[3:0]

dbg_scan_n[3:0]

Function

$2 (SCAN_N)

ARM7 Scan Chain 0 Selected

$C (INTEST)

Debug Register SC4 Selected

$8 (NEXUS_ACCESS)

n/a

Nexus Selected

PTI

ARM7

TAP State

Machine

Nexus

TCK

TMS

TDI

TDO

Synchr.

Logic

dbg_ir[3:0]

dbg_tapsm[3:0]

dbg_scan_n[3:0]

tck/tms/tdi/tdo

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