MCF548x Reference Manual, Rev. 3
23-2 Freescale Semiconductor

23.1.2 Features

The basic features of the JTAG module are the following:
Performs boundary-scan operations to test circuit board electrical continuity
Bypasses instruction to reduce the shift register path to a single cell
Sets chip output pins to safety states while executing the bypass instruction
Samples the system pins during operation and transparently shift out the result
Selects between JTAG TAP controller and Background Debug Module (BDM) using the
MTMOD0 pin

23.1.3 Modes of Operation

The MTMOD0 pin can select between the following modes of operation:
JTAG mode
BDM—background debug mode (For more information, refer to Chapter 8, “Debug Support.”)

23.2 External Signal Description

The JTAG module has five input and one output external signals, as described in Table 23-1.

23.2.1 Detailed Signal Description

23.2.1.1 Test Mode 0 (MTMOD0)

The MTMOD0 pin selects between Debug module and JTAG. If MTMOD0 is low, the Debug module is
selected; if it is high, the JTAG is selected. Table 23-2 summarizes the pin function selected depending
upon MTMOD0 logic state.
Table 23-1. Signal Properties
Name Direction Function Reset State Pull up
MTMOD0 Input JTAG/BDM selector input
TCK Input JTAG Test clock input Active
TMS/BKPT Input JTAG Test mode select / BDM Breakpoint Active
TDI/DSI Input JTAG Test data input / BDM Development serial input Active
TRST/DSCLK Input JTAG Test reset input / BDM Development serial clock Active
TDO/DSO Output JTAG Test data output / BDM Development serial output Hi-Z / 0