Freescale Semiconductor SC140 specifications Debugrequest and Enableeonce Commands

Overview of the Combined JTAG and EOnCE Interface

TDI

SC140	SC140
CORE 1	CORE n
EOnCE	EOnCE
Choose	Choose
	~ ~
JTAG
	Controls
Figure 4-3. Cascading Multiple EOnCE Modules

to TDO mux

4.2.5 DEBUG_REQUEST and ENABLE_EONCE Commands

After the CHOOSE_EONCE instruction completes, DEBUG_REQUEST and ENABLE_EONCE instructions can be executed. More than one such instruction can execute, and other instructions can be placed between them and also between them and the CHOOSE_EONCE instruction. The EOnCE modules selected in the CHOOSE_EONCE instruction remain selected until the next CHOOSE_EONCE instruction. The DEBUG_REQUEST or ENABLE_EONCE instruction is shifted in during the Shift-IR state, as are all JTAG instructions.

4.2.6 Reading/Writing EOnCE Registers Through JTAG

An external host can read or write almost every EOnCE register through the JTAG interface, using the following steps (see Figure 4-4):

1.Execute the CHOOSE_EONCE command in the JTAG.

2.Send the data showing which EOnCE is chosen. This command enables the JTAG to manage multiple EOnCE modules in a device.

3.Execute the ENABLE_EONCE command in the JTAG.

4.Write the EOnCE command into the EOnCE Command register (ECR).

That is, the host enters the JTAG TAP state machine into the shift-dr state and then gives the required command on the TDI input signal. After the command is shifted in, the JTAG TAP state machine must enter the update-dr state. The data shifted via the TDI is sampled into the ECR. For example, if the command written into the ECR is “Write EDCA0_CTRL,” then the host must again enter the JTAG into shift-dr and shift the required data, which is to be written into the EDCA0_CTRL, via TDI. If the command is “read some register,” then the DR chain must be passed again and the contents of the register are shifted out through the TDO output.

SC140 DSP Core Reference Manual 4-7