1. Processor Register Set of M16C
2 banks of general-purpose registers
4 16-bit data registers R0 - R3
Upper and lower bytes of registers R0 and R1 can be used as 8-bit registers (R0L, R0H, R1L, R1H)
2 16-bit address registers A0 & A1
Can access pairs of registers as 32-bit registers: R2R0, R3R1, A1A0
Bank 0
Data register
Bank 1 PC
Program Counter R0
データレジスタ
アドレスレジスタ
Frame base register R0 R1 R2 R3 A0 A1 FB
R0H
R0H
R0L
INTB
Interrupt table register R1
R1H
R1L R2 R3
Address register
USP
User Stack Pointer A0
ISP
Interrupt Stack Pointer A1 SB
Static base register
Frame base register FB
FLG
Flag register
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2. Bus Slave Selection Port enable (chip select)
Only one slave device is active and accepts requests from the bus
Decode address: get the most significant bits of the address
Memory Map
Port enable
0x0000
Memory 1
Master
Slave
Slave
0x4000
Memory 2
CPU
Memory 1
Memory 2
0x8000 EN EN
Address Decoder
“00” active
0x1000 :
0x2000 :
0x4000 :
0x5000 :
The upper 2 bits
Chip Select
“01” active
Address signal
16-bit
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3. Peripheral Device: Control Register
The control registers are used to set up different modes
Some features are configured by separate bits
The first step in programming peripheral devices is to understand control registers of the device
Example of the configuration register
Counter source select bit
(M16C timer)
Timer
A0 mode register
Name
Address
R/W
Access Size
Timer A0 mode register
0x0396 8
Timer A0 register
0x0387 R 16
Counter start flag
0x0380 7 6 5 4 3 2 1
TMOD0
TMOD1
MR0
MR1
MR2
MR3
TCK0
TCK1
Specify the operating mode 00: Timer mode 01: Event counter mode 10: One-shot timer mode 11: Pulse with modulation (PWM) mode
Different functions depending on the mode
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4. Peripheral Devices: Using the GPIO as an Output Port
Examples of HSB16C (speaker sound generators)
1 LED is connected to port register, lights when 1 is written
LED4 lights in C
*((char*)0x03E0) = 0x01
M16C (microcontroller)
Address
0xF000
Memory
CPU
Write memory instruction
Program PC
mov.b #1h, 03e0h
0xF120
0xF120
VCC
GPIO
Port Registers
LED4 : On … 1 1
0x03E0 … 1
LED3 : Off 1
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5. Peripheral Devices: Using the GPIO as an Input Port
Examples of HSB16C
The value of the port register is “1” when the switch is pressed.
Check SW9 in C
if(*((char*)0x03E1) & 0x20 == 0x20){… }
M16C
Address
0xF000
CPU
Memory
Read memory instruction
Program PC
mov.b 03e1h, R1
0xF120
0xF120
VCC
GPIO
Port Registers
SW9 : On 6 5 1 1
0x03E1 1
SW8 : Off 1
GND
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6. Peripheral Device: Pull-up and Pull-down
High and low voltage values (Hi and Lo) are used to determine the ‘1’ and ‘0’ digital value
Example: When the supply voltage is nearly 5v, 4 ~ 5v is Hi, 0 ~ 1v is Lo
Digital signal voltage values must be in the range of Lo or Hi
Pull-up and pull-down
Circuit configuration for stable electrical input when connecting a switch to an input GPIO port
Example of pull-up
Switch ON
Switch OFF
Port Register
Port Register
Switch
Switch
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7. Peripheral Device: Serial I/O
Set specific value to control registers to configure I/O port
Transmitter side: read value to send from special register, put it to transmit the buffer
Often FIFO is used
Receiver side: get received byte from buffer and put it to special register
To check if send or receive complete, check the status register
Transmitting side
Receiver
Control / status register
Control / status register
Transmit Buffer
Receive buffer
CPU
CPU
FIFO
FIFO
Transmission line 7 6 5 4 3 2 1 1 3 2 5 7 6 4
Shift register
Shift register
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8. Programmable Interrupt Controller (PIC)
Accept multiple interrupt requests, issue a single interrupt request to a processor
Each interrupt request can be configured to be ignored
Interrupt Source Register is used to determine what interrupt occurred
Several PICs can be used in cascade
Get interrupt information
Stores information about interrupt
Interrupt enable/disable
PIC
CPU
Source Register
Mask register
Interrupt request 1
Interrupt request 2
Interrupt request 3
Interrupt request 4
Copyright © 2011 DSR Corporation