1. Read Chapter 3 (David E. Simon, An Embedded Software Primer)
mP Based Systems
Read Chapter 3
(David E. Simon, An Embedded Software Primer)

2. Embedded Systems Development Introduction Saâd Biaz
mP Based Systems
mP based system
Address Bus mP
Digital outputs (parallel port)
LED
Memory
System
I/O
Digital inputs (parallel input)
Switch
Serial port
Analog input/output
Temperature
Sensor
Data Bus
Storage
Embedded Systems Development Introduction Saâd Biaz
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3. Embedded Systems Development Introduction Saâd Biaz
Memory and I/O mapping
Consider an 8-bit mP (imaginary) with a 6-bit address bus. First instruction to execute (after power on) is at address 48.
We have:
16B ROM components (16 x 1B)
16B RAM components (16 x 1B)
We plan to ¼ of the memory with ROM, ½ of the memory in RAM, and ¼ I/O
Embedded Systems Development Introduction Saâd Biaz
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4. Memory and I/O mapping (2)
Let us map our address space
What is the address range for the ROM space?
What is the address range for the RAM space?
What is the address range for the I/O space
A5A4A3A2A1A0
= 0
= 15
26=64
I/O
= 16
= 31
RAM 1
RAM 2
= 32
= 47
= 48
= 63
ROM
Embedded Systems Development Introduction Saâd Biaz
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5. Memory and I/O mapping (3)
1) What is the size of the address space?
2) What is the size of the address bus for the ROM and RAM components? mP
Address Bus
Data Bus 6 8 A3 A0
16B
RAM D0 D7
16B
ROM D0 D7 A3 A0
Embedded Systems Development Introduction Saâd Biaz
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6. Embedded Systems Development Introduction Saâd Biaz
Memory Wiring
A5A4 = 01
A5A4 = 10
A5A4 = 11
RAM A3 A0
D7-D0
R/W CS
RAM A3 A0
D7-D0
R/W CS
ROM A3 A0
D7-D0
R/W CS
Address Bus 8 A3 A0 A4 A5 mP
Data Bus
D7-D0
R/W
Embedded Systems Development Introduction Saâd Biaz
(4/17/2017)

7. Embedded Systems Development Introduction Saâd Biaz
Input (switch) Wiring
How to interface a switch?
First, choose the address where to map the switch
Second, build a circuit that connects the swich to data bus
only when associated address is given by mP.
VCC
RAM A3 A0
D7-D0
R/W CS
RAM A3 A0
D7-D0
R/W CS
ROM A3 A0
D7-D0
R/W CS
Address Bus 8 A3 A0 A4 A5 mP
Data Bus
D7-D0
R/W
Embedded Systems Development Introduction Saâd Biaz
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8. Embedded Systems Development Introduction Saâd Biaz
Input (switch) Wiring
Let us choose the address 0 (bit D0) to map the switch
A5A4A3A2A1A0
VCC
RAM A3 A0
D7-D0
R/W CS
RAM A3 A0
D7-D0
R/W CS
ROM A3 A0
D7-D0
R/W CS
Address Bus 8 A3 A0 A4 A5 mP
Data Bus
D7-D0
R/W D0
Embedded Systems Development Introduction Saâd Biaz
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9. Embedded Systems Development Introduction Saâd Biaz
Output (LED) Wiring
Exercise I : Interface a LED at address 1, data bus line D4
A5A4A3A2A1A0
RAM A3 A0
D7-D0
R/W CS
RAM A3 A0
D7-D0
R/W CS
ROM A3 A0
D7-D0
R/W CS
Address Bus 8 A3 A0 A4 A5 mP
Data Bus
D7-D0
R/W D4
Embedded Systems Development Introduction Saâd Biaz
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10. I/O: Device Controllers
The mP communicates with the device controller through registers accessible as if they are memory cells.
Example: a device controller with 2m registers CS
Chip
R/W
I/O
Function
Am-1 A0
D7-D0
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11. Example of Device Controllers: Parallel I/O Port
Ports A, B, and C can be configured to be inputs or outputs.
Configuration is made by writing in the 8-bit control register
After configuration, ports A,B, or C can be read or written to as if they were memory cells.
Intel 8255 8 CS RD WD A
8-bit Control Reg. B 8 A1 C 8 A0
D7-D0
Embedded Systems Development Introduction Saâd Biaz
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12. Example of Device Controllers: UART or Serial I/O Port
The 8-bit configuration register is used to select the speed (110bps to 19200bps), parity check, number of bits per word, lentgh of stop bits.
The mP writes to the data register the data to be sent serially on TX
The mP reads from the data register data received serially on RX. CS
Intel 8251 RD WD TX
8-bit Data Reg. RX
8-bit Config. Reg. A0
D7-D0
Embedded Systems Development Introduction Saâd Biaz
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13. Example of Device Controllers: Timer
The mP initializes a counter Ci with some value.
All counters are decremented at each tick of the clock input
When the counter Ci reaches 0, an impulse is output on the corresponding output Oi. CS
Intel 8253 RD WD O0
16-bit Counter 0 O1
16-bit Counter 1
CLK O2
16-bit Counter 2 A1 A0
D7-D0
8-bit Config. Reg.
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14. Direct Memory Access (DMA)
The idea is to transfer directly I/O stream to/from memory without using the CPU (long bus cycles)
Reminder, to transfer a word from I/O to memory. The mP must:
Fetch its “reading” instruction (IN AX,DX)
Decode the instruction, execute it
Fetch the “write” instruction
Test if done (involves loops/jumps..etc)
Embedded Systems Development Introduction Saâd Biaz
(4/17/2017)

15. Direct Memory Access (DMA) (2)
Transfering CONTIGUOUS data can be made more efficiently:
A counter is needed to generate increasing addresses and proper control signals to the memory.
Embedded Systems Development Introduction Saâd Biaz
(4/17/2017)

16. Direct Memory Access (DMA)
RAM mP
Address/Control Bus
Data Bus
BusAck
BusReq
I/O
DMA
Controller
DMAAck
DMAReq
Embedded Systems Development Introduction Saâd Biaz
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17. Gluing a mP-based system
Decoding functions may require some components (especially if address bus very large 32 to 64 bits).
PALs
FGPAs
Embedded Systems Development Introduction Saâd Biaz
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18. Built-Ins on Microcontrollers
Address decoding
Timers
I/O
DMA
ADC-DAC (Analog-Digital Converter … )
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19. mP Based Systems (Example: Microcontroller Rabbit 2000)
Read Chapter 1 and 2
(Rabbit Semiconductor, Rabbit 2000 Microprocessor User’s Manual)

20. Rabbit 2000 Characteristics
8-bit data bus
20-bit address bus (extensible)
Software driven system clock
2 timers
40 bit parallel configurable I/O
4 serial ports
1 watchdog timer
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21. Rabbit 2000 Characteristics (2)
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22. Embedded Systems Development Introduction Saâd Biaz
Rabbit 2000 System Clock
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23. Saving Power (By Software)
Add memory wait states
Turn off clock doubler (if in use)
Divide frequency by 8 (select f/8)
Run code in RAM, not in flash
Use for the CPU and peripheral clock the 32K oscillator (disable main oscillator)
Embedded Systems Development Introduction Saâd Biaz
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24. Embedded Systems Development Introduction Saâd Biaz
Timers
RTC: 48-bit register driven by 32K
Watchdog timer (0.25s, 0.5s, 1s, or 2s)
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25. Embedded Systems Development Introduction Saâd Biaz
Timers (2)
Embedded Systems Development Introduction Saâd Biaz
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26. Embedded Systems Development Introduction Saâd Biaz
Serial Communication
Embedded Systems Development Introduction Saâd Biaz
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