MA828
ZPP
O/Ps WSS
CS
MOTEL
INTERFACE
8
BUS
CONTROL
RED PHASE
PULSE
DELETION
PULSE
DELAY
CIRCUIT
RPHT
RPHB
SYSTEM
BUS
AD
0
-AD
7
BUS
DEMULTIPLEXER
R0
R1
R2
R3
R4
24-BIT
INITIALISATION
REGISTER
PHASING
AND
CONTROL
LOGIC
YELLOW PHASE
PULSE
DELETION
PULSE
DELAY
CIRCUIT
YPHT
YPHB
24-BIT
CONTROL
REGISTER
BLUE PHASE
RST
PULSE
DELETION
PULSE
DELAY
CIRCUIT
BPHT
BPHB
CLOCK
CLOCK
DIVIDER
ADDRESS
GENERATOR
TRIP
LATCH
TRIP
SET
TRIP
WAVEFORM
ROM
Fig. 2 MA828 internal block diagram
FUNCTIONAL DESCRIPTION
An asynchronous method of PWM generation is used with
uniform or ‘double-edged’ regular sampling of the waveform
stored in the internal ROM as illustrated in Fig. 3.
The triangle carrier wave frequency is selectable up to 24kHz
(assuming the maximum clock frequency of 12.5MHz is used),
enabling ultrasonic operation for noise critical applications. With
12.5MHz clock, power frequency ranges of up to 4kHz are
possible, with the actual output frequency resolved to 12-bit
accuracy within the chosen range in order to give precise motor
speed control and smooth frequency changing. The output
phase sequence of the PWM outputs can also be changed to
allow both forward and reverse motor operation.
PWM output pulses can be ‘tailored’ to the inverter charac-
teristics by defining the minimum allowable pulse width (the
MA828 will delete all shorter pulses from the ‘pure’ PWM pulse
train) and the pulse delay (underlap) time without the need for
external circuitry. This gives cost advantages in both component
savings and in allowing the same PWM circuitry to be used for
control of a number of different motor drive circuits simply by
changing the microprocessor software.
Power frequency amplitude control is also provided with an
overmodulation option to assist in rapid motor braking.
Alternatively, braking may be implemented by setting the
rotational speed to 0Hz. This is termed ‘DC injection braking’, in
which the rotation of the motor is opposed by allowing DC to flow
in the windings.
A trip input allows the PWM outputs to be shut down
immediately, overriding the microprocessor control in the event
of an emergency.
The Waveform Sampling Synchronisation (WSS) output
may be used in conjunction with the ZPP signals to provide
feedback of the actual rotational speed from the rotor. This is of
particular use in slip compensated systems.
Other possible MA828 applications are as a 3-phase wave-
form generator as part of a switched-mode power supply (SMPS)
or of an uninterruptible power supply (UPS). In such applications
the high carrier frequency allows a very small switching trans-
former to be used.
MICROPROCESSOR INTERFACE
The MA828 interfaces to the controlling microprocessor by
means of a multiplexed bus of the MOTEL format. This interface
bus has the ability to adapt itself automatically to the format and
timing of both MOTorola and IntEL interface buses (hence
MOTEL). Internally, the detection circuitry latches the status of
the DS/RD line when AS/ALE goes high. If the result is high.
Then the Intel mode is used; if the result is low then the Motorola
mode is used. This procedure is carried out each time that AS/
ALE goes high. In practice this mode selection is transparent to
the user. For bus connection and timing information refer to the
description relevant to the microprocessor/controller being used.
Industry standard microprocessors such as the 8085, 8088,
etc. and microcontrollers such as the 8051, 8052 and 6805 are
all compatible with the interface on the MA828. This interface
consists of 8 data lines, AD
0
- AD
7
(write-only in this instance),
which are multiplexed to carry both the address and data
information, 3 bus control lines, labelled WR,RD and ALE in Intel
mode and R/W, DS and AS in Motorola mode, and a Chip Select
input. CS, which allows the MA828 to share the same bus as
other microprocessor peripherals. It should be noted that all bus
timings are derived from the microprocessor and are independ-
ent of the MA828 clock input.
3
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
