PC87591L datasheet(261/437 Pages) NSC

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Embedded Controller Modules (Continued)

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Debug Bypass Register (BYPASS)

The BYPASS register provides a minimum length serial path for data movement between TDI and TDO. This path can be

selected when no other data register needs to be accessed.

The BYPASS register consists of a single shift register stage.

When the current instruction selects the BYPASS register for inclusion in the serial path between TDI and TDO, the shift

register stage is set to 0 on the rising edge of TCK following entry into Capture-DR state. The BYPASS register is accessed

from the JTAG serial bus only.

Debug Data Register (DBGDATA)

This register is the shift register element of DBGRXD and DBGTXD. It is accessed from the JTAG serial bus only. Figure 85

shows the parallel load data scheme.

The DBGDATA register consists of shift register stages according to the data buffer length. The actual length of the data value,

in a scan operation, is set before Capture-DR state when the current instruction is SCAN_RX or SCAN_TX. In the first case, it

is set according to SCAN_RX L0 to L4; in the latter case, it is set according to the value of MSG_LEN in DBGTXST register.

The actual length of the register is 16*(length+1), where “length” is the binary positive number created by the length field

(with L4 as MSB).

A length longer than the maximum data buffer is mapped to maximum length. A length shorter than the maximum data buffer

results in loading the data to/from the smallest addresses in the data buffer. Maximum length for this design is 128 shift reg-

ister stages. Note that TDO is always fixed; the TDI “insertion-point” changes according to the actual length.

Figure 85. DBGDATA Connection to the Data Links

Debug Abort Mask Register (DBGMASKS)

This is a serial shift register, with parallel output and parallel input (for read and write of ABORT_MASK register), accessed

by the JTAG serial bus while the SCAN_ABORT_MASK instruction is set to TAP IR. The register is not addressable from

the peripheral bus. The non-reserved bits of ABORT_MASK register are preset to 1 on Power-Up reset.

The ABORT_MASK register consists of shift register stages with 16 bits. Bits 1 to 15 are reserved and should be written with

0. A bit value of 1 enables the processor to abort; a bit value of 0 disables it.

Figure 86. ABORT_MASK and DBGMASKS Register Interaction

TDI

TDO

ADD XXE

ADD XXC

ADD XX0

ADD XX2

DBGTXD

DBGDATA

DBGRXD

ADD YYE

ADD YYC

ADD YY0

ADD YY2

Length = 1 word

Length = 8 words

TDI

TDO

ABORT_MASK

DBGMASKS

PC87591L Datasheet(PDF) 261 Page - National Semiconductor (TI)

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