NXP Semiconductors MPC5566 - Functional Description

Nexus
MPC5566 Microcontroller Reference Manual, Rev. 2
25-84 Freescale Semiconductor
Reading/writing of a Nexus register then requires two (2) passes through the data-scan (DR) path of the
JTAG state machine (refer to Chapter 24, “IEEE 1149.1 Test Access Port Controller (JTAGC)”).
1. The first pass through the DR selects the Nexus register to be accessed by providing an index
(refer to Table 25-46), and the direction (read/write). This is achieved by loading an 8-bit value into
the JTAG data register (DR). This register has the following format:
2. The second pass through the DR then shifts the data in or out of the JTAG port, lsb first.
a) During a read access, data is latched from the selected Nexus register when the JTAG state
machine passes through the capture-DR state.
b) During a write access, data is latched into the selected Nexus register when the JTAG state
machine passes through the update-DR state.
25.17.3 Functional Description
25.17.4 Enabling NXDM Operation
The NXDM module is enabled by loading a single instruction (ACCESS_AUX_TAP_DMA as shown in
Table 25-4) into the JTAG instruction register (IR), and then loading the corresponding OnCE OCMD
register with the NEXUS_ACCESS instruction (refer to Table 25-5). After it is enabled, the module is
ready to accept control input via the JTAG pins.
The Nexus module is disabled when the JTAG state machine reaches the test-logic-reset state. This state
can be reached by the assertion of the JCOMP pin or by cycling through the state machine using the TMS
pin. The Nexus module is also disabled if a power-on reset (POR) event occurs.
If the NXDM module is disabled, no trace output is provided, and the module disables (drive inactive)
auxiliary port output pins (MDO[11:0], MSEO[1:0], MCKO). Nexus registers are not be available for
reads or writes.
Access: R/W
76543210
R
Nexus Register Index R/W
W
Reset
Figure 25-65. JTAG DR for NEXUS Register Access
Table 25-55. DR Read/Write Encoding
Nexus Register Index Description
Read/Write (R/W) 0 Read
1Write