AN2372 Freescale Semiconductor / Motorola, AN2372 Datasheet - Page 3

• Manufacturer Part Number: AN2372
• Description: Using the Output Compare TPU Function (OC) with the MPC500Family
• Manufacturer: Freescale Semiconductor / Motorola

2.2
In continuous mode, the OC function generates a continuous square wave with a 50% duty cycle after
receiving a link service request. It calculates the value of the pulse width at each link. At initialization, the
TBS field determines the time base of the channel, and the PSC field determines the initial level. The PSC
should usually be set to 11 (do not force any state), unless two or more channels executing continuous pulse
mode are required to be synchronized.
In this case, both PSC fields should be set to the same value (01 to force pin high, or 10 to force pin low)
to produce two signals in phase, or set to opposite values to produce two signals 180 degrees out of phase.
The PAC fields must also be set to appropriate values to keep the two channels synchronized. In a channel
that has a PSC value set to 01 (force pin high), the PAC field should be set to 001 (force high on match). For
a second channel to produce a complementary output, the PSC should be set to 10 (force pin low) and the
PAC field to 010 (force low on match).
Continuous pulse generation does not begin until the channel receives the first link after initialization. When
the first link is received, this function places the value pointed to by REF_ADDR into both the event register
and the REF_TIME parameter. Each link, including the first, computes a new value for OFFSET as
OFFSET = (REF_ADDR2) * RATIO
where () indicates the value pointed to by the address specified. OFFSET must be less than 0x8000 for
proper operation.
When a match event occurs, OFFSET is added to the value in REF_TIME to form the next pulse edge, and
this value replaces the value in REF_TIME. On all links subsequent to the first link, the value in REF_TIME
is replaced with the value pointed to by REF_ADDR1. REF_ADDR and REF_ADDR1 can point to either
a value updated by the linking channel or to the most recent match event value. This capability to reference
parameters in another channel allows the OC function to be synchronized to a channel performing either a
PPWA or ITC function. This allows the user to perform synchronized frequency multiplication or division
of an input signal. Figure 2 clarifies this capability.
MOTOROLA
Continuous Pulse Mode
(REF_ADDR1)
(REF_ADDR1)
B) IMMEDIATE OUTPUT NOT SELECTED
A) IMMEDIATE OUTPUT SELECTED
Freescale Semiconductor, Inc.
Figure 1. Host-Initiated Pulse Mode Diagram
For More Information On This Product,
Using the Output Compare TPU Function
OFFSET
OFFSET
Go to: www.freescale.com
REF_TIME = (REF_ADDR1) + OFFSET
REF_TIME = (REF_ADDR1) + OFFSET
Continuous Pulse Mode
3