RM0390 Rev 4 1289/1328
RM0390 Debug support (DBG)
1318
33.5 STM32F446xx JTAG TAP connection
The STM32F446xx MCUs integrate two serially connected JTAG TAPs, the boundary scan
TAP (IR is 5-bit wide) and the Cortex
®
-M4 with FPU TAP (IR is 4-bit wide).
To access the TAP of the Cortex
®
-M4 with FPU for debug purposes:
1. First, it is necessary to shift the BYPASS instruction of the boundary scan TAP.
2. Then, for each IR shift, the scan chain contains 9 bits (=5+4) and the unused TAP
instruction must be shifted in using the BYPASS instruction.
3. For each data shift, the unused TAP, which is in BYPASS mode, adds 1 extra data bit in
the data scan chain.
Note: Important: Once Serial-Wire is selected using the dedicated Arm
®
JTAG sequence, the
boundary scan TAP is automatically disabled (JTMS forced high).
Figure 444. JTAG TAP connections
"OUNDARYSCAN
4!0
.*4234
#ORTEX-4!0
*4-3
4-3 N42344-3 N4234
*4$)
*4$/
4$) 4$/ 4$) 4$/
37$0
34-&XXX
3ELECTED
)2ISBITWIDE )2ISBITWIDE
-36
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