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Course Introduction
Purpose
This course provides an overview of the peripheral functions that are built into
M16C series microcontrollers (MCUs).
Objectives
 Learn about the features and operation of the Analog-to-Digital converter,
Digital-to-Analog converter, DMA Controller, CRC calculation circuit, and
Watchdog Timer.
 Understand the basics of the interrupts M16C MCUs provide.
 Discover how the clock generation circuit and voltage detection circuit
operate.
Content
24 pages
4 questions
Learning Time
38 minutes
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Analog-to-Digital Converter
Successive-approximation A/D converter circuit
24 channels
10-bit or 8-bit resolution, selectable
Built-in Sample & Hold
Five operating modes:
- One Shot
- Repeat
- Single Sweep
- Repeat Sweep, Modes 0 and 1
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Successive-Approximation Circuit
fAD
VREF
VCUT=0
AVssVCUT=0
Resistor
R-2R
Ladder
Resistor Ladder
ADCON1
Successive conversion register
ADCON0
AD0 Register
AD1 Register
AD2 Register
AD3 Register
AD4 Register
Decoder for
A-D Register
Vref
AD5 Register
Vin
AD6 Register
Comparator
AD7 Register
Data Bus High Order
Data Bus Low Order
AN00-07
AN20-27
AN0-7
ADCON2
Decoder for
channel selection
Multiplexor
Multiplexor
fAD
Multiplexor
ANEX0
ANEX1
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Clock Divider Circuit
¸1, ¸2, ¸¸3, ¸4, ¸6, ¸12
A/D Operating Modes
Mode
Description
One Shot mode
One analog input channel is converted to a digital value once.
The conversion is stopped when it is completed or if the Start
flag is set back to zero. At the end of the conversion, an
interrupt request can be generated.
Repeat mode
Continuous conversions can be performed on an analog input.
The conversion is stopped by clearing the AD Conversion Start
flag. No interrupt request is generated in this mode.
Single Sweep mode
The input voltages on selected pins are converted once, one at
a time. You select the signals to be converted using the
ADCON0 and ADCON1 registers. Conversion is ended by
clearing the ADST bit to 0 or when the conversion is complete.
An end-of-conversion interrupt can be generated.
Repeat Sweep modes
The analog signals on multiple channels are converted to digital
values repeatedly, one at a time. This mode actually
encompasses two modes: modes 0 and 1, which we will
discuss on the next page.
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A/D Sweep Modes
M16C ADC
Single Sweep Mode* – 8 pins
AD C
S a m pling
AD
AN0
AN1
AN2
AN3
AN4
AN5
AN6
AN7
S tart
AN0
AD0
AN1
AD1
AN2
AD2
AN3
AD3
AN4
AD4
AN5
AD5
AN6
AD6
AN7
AD7
8/10-bit
Repeat Sweep Mode 0– 8 pins
AD C
S a m pling
AD
AN0
AN1
AN2
AN3
AN4
AN5
AN6
AN7
AN0
AN1
AN2
AN3
AN4
AN5
AN6
AN7
AN0
AN1
AN6
AN0
S tart
Repeat Sweep Mode 1– 8 pins (priority on 2 pins: AN0, AN1)
AD C
S a m pling
AD
AN0
AN1
AN2
AN0
AN1
AN3
AN0
AN1
AN4
AN0
AN1
AN5
S tart
* In Single Sweep mode, an A/D interrupt is generated after the conversion is complete.
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PROPERTIES
On passing, 'Finish' button:
On failing, 'Finish' button:
Allow user to leave quiz:
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Digital-to-Analog Converter
R-2R type D/A converter
Two separate independent converters
8-bit resolution
Voltage reference (VREF) input is available so the output
value can be easily scaled.
Control register
DA register
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Direct Memory Access Controller
Two DMAC channels
Transfers
 Any fixed address to/from the 1MB space
 Any fixed address to/from fixed address
Transfers can be up to 128KB (16-bit) or 64KB (8-bit)
Request sources
 INT0/1, SI/O3, SI/O4
 Timers A0-A4, B0-B5
 UART0-2, A/D, Software Trigger
8-bit and 16-bit transfer units
Single and Repeat transfer modes
Cycle-steal operation
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Single and Repeat Transfers
Single Transfer
 A byte (8-bit) or word (16-bit) is transferred per request.
 Transfers stop when:
- DMAC channel is disabled (DMAE set to “0”).
- DMAi transfer counter underflows when the terminal count
is reached.
Repeat Transfer
 A byte (8-bit) or word (16-bit) is transferred per request.
 When the DMAi counter underflows, it is reloaded with the
value of DMAi transfer counter reload register, then DMAC
transfers continue.
 Transfers stop when:
- DMAC channel is disabled (DMAE set to “0”).
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CRC Circuit
Cyclic Redundancy Check circuit generates
checksum (CRC value) for a block of data that can
be used to detect errors in the data.
16-bit CRC value is generated from 8-bit values
(bytes) input to CRC circuit.
Dedicated hardware CRC circuit consists of two
registers:
 CRCD: 16-bit register that contains the calculated CRC
 CRCIN: 8-bit register that is loaded with the 8-bit data used
to produce the CRC
CRC circuits in M16C MCUs use CRC-CCITT
generator polynomial (X16 + X12 + X5 + 1) to calculate
CRC value.
CRC code generation takes two cycles per byte of
data.
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Watchdog Timer
WDT can Reset MCU if application software goes out of control.
- In Watchdog Reset mode, the WDT counter value must be re-written
periodically by user application to prevent underflows.
15-bit counter
Clock sources include the CPU clock, PLL clock, and ring
oscillator.
Two operating modes:
- Interrupt request—When counter underflows, an interrupt is generated.
- Reset request—When counter underflows, MCU is reset.
Pre-scaler
1/16
PM22=0
CPU Clock
PM12=0
Watchdog Timer
interrupt request
1/16
Watchdog Timer
/HOLD
PM22=1
1/16
Write to WDTS register
Ring oscillator circuit
PM22=0
Set to H’7FFF
/RESET
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Reset
PROPERTIES
On passing, 'Finish' button:
On failing, 'Finish' button:
Allow user to leave quiz:
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Interrupts
M16C MCUs support software and hardware interrupt types.
Undefined instruction (UND instruction)
Overflow (INTO instruction)
BRK instruction
INT instruction
Software
(Non-maskable interrupt)
Interrupt
Special
(Non-maskable interrupt)
Hardware
NMI
/DBC (debug tools only)
Watchdog Timer
Oscillation stop and re-oscillation detection
Single step (debug tools only)
Address match
Peripheral function
(Maskable interrupt)
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Software Interrupts
Interrupts
Description
Overflow interrupt
Occurs when executing the INTO instruction with the “O” flag set. The
“O” flag is changed by arithmetic. If the “O” bit in the CPU’s FLG
register is set to “1” when the INTO (“O” test instruction) is executed,
then the Overflow interrupt will be generated. The “O” bit can be set
by the following arithmetic instructions: ABS, ADC, ADCF, ADD, CMP,
DIV, DIVX, NEG, RMPA, SBB, SHA, and SUB.
BRK interrupt
The BRK interrupt occurs when the “BRK” instruction is executed.
This instruction is useful in debugging applications where it
implements breakpoint functionality.
INT instruction
interrupt (also known as
a software trap)
When the INT instruction with an interrupt vector number is executed,
the corresponding vector is read and the relevant interrupt service
routine (ISR) executes. The INT or trap interrupt can be used to
generate a software interrupt that is particularly useful in real-time
operating system (RTOS) implementations for task switching.
Undefined instruction
interrupt
The Undefined instruction interrupt occurs when executing the UND
instruction.
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Hardware Interrupts
Special, non-maskable interrupts
 NMI is generated when NMI pin changes from high to low.
 Voltage-down detection is provided by LVD circuit.
 Watchdog Timer is generated when WDT operates in
interrupt request mode.
 Oscillation stop and re-oscillation detection are provided
by the clock generation circuit.
 DBC is normally only used by development tools.
 Single step is normally only used by development tools.
 Address match is generated immediately before an
instruction whose address matches a specified value.
Peripheral function interrupts, maskable
 Generated by timers, A/D, and other on-chip functions
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Interrupt Characteristics
An interrupt vector (4 bytes) contains the start of that
interrupt’s interrupt service routine (ISR).
Part of the vector table is fixed (addresses 0xFFFDC to 0xFFFF)
and contains the software interrupt vectors and special
non-maskable hardware interrupt vectors.
The remaining vectors can be located elsewhere in the memory;
start address of the table is loaded into CPU’s INTB register.
There are eight priority levels: 0 to 7 (lowest to highest).
Interrupt sequence:
1.
CPU clears interrupt’s IR flag to “0”.
2.
CPU FLG register stored in CPU temporary register.
3.
FLG registers configured as follows:
I = 0, D = 0, U = 0 (unless INT for interrupts 32 to 63).
4.
CPU temporary register and PC are copied to stack.
5.
Interrupt’s priority level is set in the CPU’s IPL register.
6.
PC is loaded with the address of the ISR
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PROPERTIES
On passing, 'Finish' button:
On failing, 'Finish' button:
Allow user to leave quiz:
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Clock Generation Circuit
The M16C clock generation circuit contains four oscillator circuits.
Use of
clock
Clock frequency
Usable
oscillator
Main clock
oscillation
circuit
• CPU clock
source
• Peripheral
function clock
source
0 to 16MHz
• Ceramic
oscillator
• Crystal osc.
Sub-clock
oscillation
circuit
• CPU clock
source
• Timer A,
Timer B clock
source
32kHz
• Crystal
oscillator
Ring oscillator
PLL frequency
synthesiser
• CPU clock source
• Peripheral function
clock source
• CPU & peripheral
clock source when
main clock stops
• CPU clock source
• Peripheral
function
clock source
About 1MHz
10 to 24MHz
-
-
Pins to connect
to oscillator
Xin, Xout
Xin, Xout
-
-
Oscillator stop,
restart function
Presence
Presence
Presence
Presence
Oscillator
status after
reset
Oscillating
Stopped
Stopped
Stopped
-
-
Other
Externally derived clock can be input
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Clock Circuit and Normal Mode
 Three Modes: Normal, Wait, and Stop
 Normal operating mode has 7 sub-modes:
- High-speed
- PLL operation
- Medium-speed
- Low-speed
- Low-power dissipation
- Ring oscillator
- Ring oscillator low-power dissipation
Clock Generation Circuit of M16C MCUs
Main clock
generator
Sub-clock
generator
Osc. stop,
re-start
detection
Frequency Divider
a
PLL
e
1/2
b
1/2
1/2
c
1/2
1/2
1/32
1/2
1/4
1/8
1/16
Ring
oscillator
d
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Clock Circuit - Wait Mode
In Wait mode, the CPU clock is turned off to save power.
Peripherals can be supplied by the main clock, sub-clock, ring oscillator,
and PLL clock.
Main clock supply to the peripheral functions can be switched off
and the peripherals can be driven from the 32kHz sub-clock.
Wait mode is entered by executing the WAIT instruction.
Disabling the PLL before entering Wait mode further reduces power
consumption.
Pin states during Wait mode are defined. (Specific details can be found in
the M16C hardware manuals.)
Wait mode is exited by a hardware reset, NMI, or peripheral interrupt.
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Clock Circuit - Stop Mode
In Stop mode, all oscillator clocks are stopped.
The CPU and the peripherals supplied from these clocks also stop.
Any peripherals supplied by external clocks continue to operate.
This mode minimizes power consumption.
If the Vcc pins are supplied with a voltage ≥VRAM, the contents of
the internal RAM are retained.
Stop mode is entered by turning all clocks off by setting the
CM10 bit in the CM1 register to “1”.
Pin states during Stop mode are defined. (Specific details are in the
M16C hardware manuals.)
Stop mode is exited by a hardware reset, NMI, or peripheral interrupt.
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Clock-Generator Mode Transitions
Reset
All oscillators stopped
CPU operation stopped
Wait
instruction
CM10=1
Stop mode
Interrupt
CM07=0
CM06=1
CM05=0
CM11=0
CM00=1
Medium-speed mode
(divided by 8 mode)
High-speed, mediumspeed mode
CM10=1
When
When
low-power lowdissipation speed
mode
mode
CM10=1
Stop mode
Interrupt
CM10=1
Stop mode
Wait mode
Wait
instruction
Interrupt
Stop mode
Interrupt
Interrupt
Wait mode
PLL mode
Low-speed, low-power
dissipation mode
Ring oscillator, ring
oscillator low-power
dissipation mode
Interrupt
Wait
instruction
Wait mode
Interrupt
Wait
instruction
Wait mode
Interrupt
Normal mode
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PROPERTIES
On passing, 'Finish' button:
On failing, 'Finish' button:
Allow user to leave quiz:
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Voltage Detection Circuit
The voltage detection circuit monitors the input voltage at the Vcc1.
The circuit can detect the following conditions:
 Voltage down (<4.0v)
 RAM retention voltage down (<2.0v)
Should the voltage fall below 2.7v, a Reset signal can be generated.
Vcc
5.0
RESET
de-asserted
Voltage detection function activated by software
Warm start
Voltage-down
interrupt
Data backup
possible
4.0
2.7
2.0
RESET
RAM retention voltage
flag (changes from 1 to 0)
0
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RESET
de-asserted
Course Summary
Analog-to-digital converter (A/D)
Digital-to-analog converter (D/A)
Direct memory access controller (DMAC)
CRC calculation circuit
Watchdog Timer (WDT)
Interrupts
Clock generation circuit
Voltage detection circuit
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