Freescale Semiconductor StarCore SC140 - Manual (Page 117)

Overview of the Combined JTAG and EOnCE Interface
SC140 DSP Core Reference Manual 4-7
Figure 4-3. Cascading Multiple EOnCE Modules
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.
Choose
TDI
Controls
JTAG
CORE 1
~ ~
EOnCE
Choose
CORE n
EOnCE
SC140 SC140
to TDO mux