MPC563XM Reference Manual, Rev. 1
1380
Freescale Semiconductor
Preliminary—Subject to Change Without Notice
32.5.4
Nexus JTAG Port Sharing
Each of the individual Nexus blocks on the device implements a TAP controller for accessing its registers.
When Nexus has ownership of the TAP, only the block whose NEXUS-ENABLE instruction is loaded has
control of the TAP. This allows the interface to all of these individual TAP controllers to appear to be a
single port from outside the device. If no register is selected as the shift path for a Nexus block, that block
acts like a single-bit shift register, or bypass register.
32.5.5
MCKO and ipg_sync_mcko
MCKO is an output clock to the development tools used for the timing of MSEO and MDO pin functions.
MCKO is derived from the system clock and its frequency is determined by the value of the MCKO_DIV
field in the PCR. Possible operating frequencies include one-half, one-quarter, and one-eighth system
clock speed.
The NPC also generates an MCKO clock gating control output signal, nex_mcko_g_ctrl. This output can
be used by the MCKO generation logic to gate the transmission of MCKO when the auxiliary port is
enabled but not transmitting messages. The setting of the MCKO_GT bit inside the PCR determines
whether or not MCKO gating control is active. The MCKO_GT bit resets to a logic 0. In this state
nex_mcko_g_ctrl is held asserted (logic 1), and gating of MCKO is disabled. To enable gating of MCKO,
the MCKO_GT bit in the PCR is written to a logic 1. When enabled, nex_mcko_g_ctrl will negate anytime
the NPC is in enabled mode but not actively transmitting messages on the auxiliary output port, indicating
to the MCKO generation logic that MCKO can be gated at this time.
32.5.6
EVTO Sharing
The NPC block controls sharing of the EVTO output between all Nexus clients that produce an EVTO
signal. The NPC assumes incoming EVTO signals will be asserted for one system clock period. After
receiving a single clock period of asserted EVTO from any Nexus client, the NPC latches the result, and
drives EVTO for one MCKO period on the following clock. When there is no active MCKO, such as in
disabled mode, the NPC drives EVTO for two system clock periods. EVTO sharing is active as long as the
NPC is not in reset.
32.5.7
Nexus Reset Control
The JCOMP input that is used as the primary reset signal for the NPC is also used by the NPC to generate
a single-bit reset signal for other Nexus blocks. If JCOMP is negated, an internal reset is asserted,
indicating that all Nexus modules should be held in reset. nex_reset_b is also asserted when in power-on
reset. The single bit reset signal functions much like the IEEE 1149.1-2001 defined TRST signal and
allows JCOMP reset information to be provided to the Nexus blocks without each block having to monitor
JCOMP.
32.5.8
System Clock Locked Indication
Following a power-on reset, MDO[0] can be monitored to provide the lock status of the system clock.
MDO[0] is driven to a logic 1 until the system clock achieves lock after exiting power-on reset. Once the