DSP56857 datasheet(471/662 Pages) FREESCALE

471 / 662 page

JTAG Port Architecture

JTAG Port, Rev. 4

Freescale Semiconductor

17-9

functionality. Data latched into the BSR during the Capture-DR controller state may not

match the drive state of the package signal if the system requiring pull-ups are not present

within the test environment.

2. The second function of the SAMPLE/PRELOAD instruction is to initialize the BSR

output cells (PRELOAD) prior to selection of the CLAMP or EXTEST instruction. This

initialization ensures known data appears on the outputs when executing EXTEST. The

data held in the Shift register stage is transferred to the output latch on the falling edge of

TCK in the update Data Register (DR) controller state. Data is not presented to the pins

until the CLAMP or EXTEST instruction is executed.

Note:

Since there is no internal synchronization between the JTAG clock (TCK) and the

system Clock (CLK), some form of external synchronization to achieve meaningful

results when sampling system values using the SAMPLE/PRELOAD instruction must

be provided.

17.5.2.1 Identification Code Instruction (IDCODE)

The IDCODE instruction enables the IDREGISTER between TDI and TDO. It is provided as a

public instruction to allow the manufacturer part number and version of a component to be

determined through the TAP.

17.5.2.2 TAP Linking Module Select (TLM_SEL)

TLM_SEL instruction is a user-defined JTAG instruction. It is used to disable the Master TAP

and enable the TAP Linking Module (TLM). The TLM provides a means of connecting one or

more TAPs in a multi-TAP design, responding to the IC’s test pins in IEEE 1149.1 scan

operations. TLM serves as a community data register used to set the TAP linking configuration

desired. The TLM register is a 4-bit register, illustrated in Figure 17-3, and enabled between TDI

and TDO during a shift Data Register (DR) operation. It is updated on the Update DR operation.

Table 17-3. TLM Register

Update DR (Load)

Shift DR (Capture)

Bit

Master TAP

N/A

56800E TAP

N/A

N/C

N/A

N/C

N/A

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