Pin Connect Block 1 Pin Limited Processors tend to be severely pin limited Way more functions available than is practical to connect individually to IO pins Highend packages may have over 1000 pins ID: 366467
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ECE 425
Pin Connect Block
1Slide2
Pin Limited
Processors tend to be severely pin limited.Way more functions available than is practical to connect individually to I/O pins.
High-end packages may have over 1000 pins
Difficult to manufacture boards for them.
For “difficult,” read “expensive.”Inexpensive packages (like LPC2148 used in lab) have a small number of pins.
2Slide3
Multi-Function Pins
Solution is to multiplex pin functions.That’s always been done to some extent.
Example: Intel Address/Data
Mux
Bus, Motorola GPIO/TimerARM/LPC takes it much farther than 80’s architecture like 8051, HC12, etc.Implication is that it may be impractical to use some modules simultaneously.
3Slide4
Timer I/O
ARM timer needs to be able to read triggers from external world and send signals to external devices.
By default,
timer is not connected to any pins
.Must be connected via Pin Connect Block.This needs to be done before timer functions & interrupts are enabled.Pins connected to timer functions then become unavailable for GPIO, etc.
4Slide5
Pin Select Registers
Two 32-bit registers used to define functions that will be connected to pins.Two bits per pin, up to 4 totally different uses for some pins.
Third control register primarily used to put I/O into debug/trace modes.
Most programmable pins default to GPIO.
Not all pins are programmable. VCC, Reset, etc.
5Slide6
Pin Select 0 Register Snippet
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Pin Select Registers
Pin select addresses:PINSEL0: 0xE002 C000
PINSEL1 - 0xE002 C004
Now still need to associate
Px.y with something physical.Look on pin diagram of device being used.
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Timer 0 Capture 0
Connect it to a pin by writing binary 10 to bits 5:4 of Pin Select Register 0, address 0xE002_C000.
That would be 00000020
h
if all other bits are zerosThen in the hardware design the input from the sensor is connected to Pin 22.
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