
MOTOROLA
TIME PROCESSOR UNIT
MC68336/376
11-12
USER’S MANUAL
Multiple PWMs generated by MCPWM have two types of high time alignment: edge
aligned and center aligned. Edge aligned mode uses n + 1 TPU channels for n PWMs;
center aligned mode uses 2n + 1 channels. Center aligned mode allows a user-defined
“dead time” to be specified so that two PWMs can be used to drive an H-bridge without
destructive current spikes. This feature is important for motor control applications.
Refer to TPU programming note
Multichannel Pulse-Width Modulation (MCPWM)
TPU Function (TPUPN05/D) for more information.
11.5.6 Fast Quadrature Decode (FQD)
FQD is a position feedback function for motor control. It decodes the two signals from
a slotted encoder to provide the CPU32 with a 16-bit free running position counter.
FQD incorporates a “speed switch” which disables one of the channels at high speed,
allowing faster signals to be decoded. A time stamp is provided on every counter up-
date to allow position interpolation and better velocity determination at low speed or
when low resolution encoders are used. The third index channel provided by some en-
coders is handled by the NITC function.
Refer to TPU programming note
Fast Quadrature Decode (FQD) TPU Function
(TPUPN02/D) for more information.
11.5.7 Universal Asynchronous Receiver/Transmitter (UART)
The UART function uses one or two TPU channels to provide asynchronous serial
communication. Data word length is programmable from one to 14 bits. The function
supports detection or generation of even, odd, and no parity. Baud rate is freely pro-
grammable and can be higher than 100 Kbaud. Eight bidirectional UART channels
running in excess of 9600 baud can be implemented.
Refer to TPU programming note
Universal Asynchronous Receiver/Transmitter
(UART) TPU Function (TPUPN07/D) for more information.
11.5.8 Brushless Motor Commutation (COMM)
This function generates the phase commutation signals for a variety of brushless mo-
tors, including three-phase brushless DC motors. It derives the commutation state di-
rectly from the position decoded in FQD, thus eliminating the need for hall effect
sensors.
The state sequence is implemented as a user-configurable state machine, thus
providing a flexible approach with other general applications. An offset parameter is
provided to allow all the switching angles to be advanced or retarded on the fly by the
CPU32. This feature is useful for torque maintenance at high speeds.
Refer to TPU programming note
Brushless Motor Commutation (COMM) TPU Func-
tion (TPUPN09/D) for more information.
336376UMBook Page 12 Friday, November 15, 1996 2:09 PM