The document discusses various peripherals that can be used on microcontrollers for communicating with external devices. It describes peripherals such as parallel and serial input/output ports, analog-to-digital converters, digital-to-analog converters, pulse-width modulators, timers/counters, and universal asynchronous receiver/transmitters. Specific registers and parameters for configuring and controlling these peripherals on a microcontroller are also outlined.

1. Chapter 3
Assembly
Programming II
Peripherals on Microcontrollers are its means of communicating with the external world and
execute some special tasks, the most commons are: Parallel Input-Output Ports (P0-3), ADC, DAC,
PWM, SPI, I2C, Timers/Counters, UART, Voltage Reference, PLL, SFR, Dual Data Pointers, Power
Supply Monitor, Watchdog Timer, Time Interval Counter, among others

2. Assembly Programming………………….…………….…….………. 1
General Purpose Input-Output Ports (P03)…….…………………..……1
Phase Lock Loop (PLL).………..…..………………………………….2
Timers/Counters.………..………..…………………………………2
Digital to Analog Converters (DAC).……………………...…………….5
Pulse-Width Modulator (PWM).……………………...……………….8
Analog to Digital Converters (ADC).…………………….....…………10
UART Serial Interface.…………………….………….....…………12

3. The Microconverter uses four input/output ports to exchange data with external devices:
✓ P0: Port 0 is an 8-Bit Open-Drain Bidirectional I/O Port, external pull-up resistors are therefore required
when Port 0 pins are used as general-purpose outputs.
✓ P1: Port 1 is an 8-bit input port only. Unlike other ports, Port 1 defaults to Analog Input Mode. To
configure any Port 1 pin as a Digital Input, write a 0 to the Port 1 bit.
✓ P2: Port 2 is a bidirectional port with internal pull-up resistors.
✓ P3: Port 3 is a bidirectional port with internal pull-up resistors.
Open Drain: A transistor connects to low and nothing else. Open drain is useful when multiple gates or pins are
connected together with an external pull-up. If all the pins are high, they are all open circuits and the pull-up
drives the pins high. If any pin is low they all go low as they tied together. This configuration effectively forms an
AND gate. Open drain output circuits must be complemented with a “Pull-Up-Resistor” to function properly. The
open drain commonly used to drive devices such as Relays or Motors which require higher operating voltages
than the usual 5-volt logic supply. Below, connection of 12V Relay.
General Purpose Input-Output Ports (P0-3)
Assembly Programming
P0
P2
P3
P1
1

4. The ADuC842 are intended for use with a 32.768 kHz watch crystal. A PLL locks onto a multiple (512) of this to
provide a stable 16.777216 MHz clock for the system. The default core clock is the PLL clock divided by 8 or
2.097152 MHz. The core clock can be changed changing the CD bits in PLLCON (PLL control register)
The maximum core clock (16.777216 MHz) can be obtained with PLLCON = 40H
The Timer/Counter is a 16-bit register. Each timer/counter consists of two 8-bit registers: THx and TLx (x = 0, 1, and 2).
All three can be configured to operate in one of two modes:
✓ Timers: The TLx register is incremented every core clock period. Thus, one can think of it as counting clock
periods.
✓ Counters: The TLx register is incremented by a 1-to-0 transition at its corresponding external input pin: T0, T1,
or T2.
User configuration and control of all timer operating modes is achieved via three SFRs:
TMOD: Configuration for Timers 0 and 1
GATE: “0” enable Timer/Controlx when /INTx pin is high and TRx is set (x = 0 and 1)
“1” enable Timer/Controlx TRx is set (x = 0 and 1)
C/T: “0” select timer operation (input from internal system clock)
“1” select counter operation, input from Tx pin (x = 0 and 1)
M1, M0: Timer Mode Select
0 0: THx operates as an 8-bit timer/counter. TLx serves as 5-bit prescaler
0 1: 16-Bit Timer/Counter. THx and TLx are cascaded; there is no prescaler.
1 0: 8-Bit Autoreload Timer/Counter. THx holds a value that is to be reloaded into TLx each time it overflows
1 1: See User Manual
Phase Lock Loop (PLL)
Timers/Counters
Assembly Programming
0 1 0 0 0 CD2 CD1 CD0
16.777216 MHz 0 0 0
8.388608 MHz 0 0 1
4.194304 MHz 0 1 0
2.097152 MHz 0 1 1
1.048576 MHz 1 0 0
0.524288 MHz 1 0 1
0.262144 MHz 1 1 0
0.131072 1 1 1
T/C 1 T/C 0
GATE C/T M1 M0 GATE C/T M1 M0
2

5. TCON: Control for timers 0 and 1
TFx: Cleared by hardware when the PC vectors to the ISR
Set by hardware on a Timer/Counter x overflow (x = 0 and 1)
TRx: Cleared by the user to turn off Timer/Counter x.
Set by the user to turn on Timer/Counter x.
NU: These bits are not used in the control of Timer/Counter 0 and 1. Used for control of external interrupts pins.
T2CON: Timer/Counter 2 Control Register
TF2: Cleared by user software.
Set by hardware on a Timer/Counter 2 overflow.
EXF2: Cleared by user software.
Set by hardware when a reload/capture is caused by a negative transition on T2EX and EXEN2 = 1.
RCLK: Set by the user to enable the serial port.
Cleared by the user to enable Timer 1 overflow to be used for the receive clock.
TCLK: Set by the user to enable the serial port.
Cleared by the user to enable Timer 1 overflow to be used for the transmit clock.
EXEN2: Set by the user to enable a capture or reload to occur as result of a negative transition on T2EX.
Cleared by the user for Timer 2 to ignore events at T2EX.
TR2: Set by the user to start Timer 2.
Cleared by the user to stop Timer 2.
CNT2: Set by the user to select counter function (input from external T2 pin).
Cleared by the user to select timer function (input from on-chip core clock).
CAP2: Set by the user to enable captures on negative transitions at T2EX if EXEN2 = 1.
Cleared by the user to enable auto reloads with Timer 2 overflows or negative transitions at T2EX.
To compute the values of 16-bit timer/ counters (THx and TLx, x = 0, 1 and 2), can be used:
Timer: THxTLx = 65536 – Tdes*Fclk
where: Tdes = Desired interrupt time (sec)
Fclk = Frequency of core clock (Hz, defined in PLLCON)
Example: Tdes = 1msec; 16777216 Hz  THxTLx = 48759  BE77H
Counter: THxTLx = 65536 – N
where: N =Number of 1-to-0 transition in Tx (x = 0, 1 and 2)
Example: N = 5 transitions (2msec/transition)  THxTLx = 65531  FFFBH (Interrupt/10msec)
The next program tests the Timer/Counters
Assembly Programming
T/C 1 T/C 0
TF1 TR1 TF0 TR0 NU NU NU NU
TF2 EXF2 RCLK TCLK EXEN2 TR2 CNT2 CAP2
3

6. Nano 5 Card
Timer/Counter 2: Timer, 1msec, 16 bits Autoreload (Output: P2.0)
Assembly Programming
4

7. The Microconverter incorporates two 12-bit voltage output DACs on chip. Each has two selectable ranges, 0 V to
VREF (internal 2.5 V reference) and 0 V to AVDD. Both DACs share a control register, DACCON, and four data
registers, DAC1H, DAC1L, DAC0H, and DAC0L.
DACCON: DAC Control Register
Mode: Cleared = 12-bit mode.
Set = 8-bit mode (write eight bits to DACxL SFR, x = 0 and 1).
RNG1: Cleared = DAC1 range 0V − VREF.
Set = DAC1 range 0V − AVDD.
RNG0: Set = DAC0 range 0V − AVDD.
Cleared = DAC0 range 0V − VREF.
CLR1: Set = DAC1 output normal.
Cleared = DAC1 output forced to 0 V.
CLR0: Set = DAC0 output normal.
Cleared = DAC0 output forced to 0 V.
SYNC: Set = DAC outputs update as soon as DACxL SFRs are written.
Cleared = User can simultaneously update both DACs.
PD1: Set = power on DAC1.
Cleared = power off DAC1.
PD0: Set = power on DAC0.
Cleared = power off DAC0.
Timer/Counter 1: Counter, 5 transitions 1-0 (2msec) in T1 (Output: P2.1)
Timer/Counter 0: Timer 16 bits, 1msec, Counter: 200 (Output: P2.0)
Digital to Analog Converters (DAC)
Assembly Programming
Mode RNG1 RNG0 CLR1 CLR0 SYNC PD1 PD0
5

8. The following program compute the codes that generates a sinusoidal function
Assembly Programming
6

9. After Reset, the CFG842 register is 00H, then the DAC output buffer is active. The example of assembler program,
using DAC1 as sine generator is shows below
7
Assembly Programming

10. The PWM uses five SFRs: PWMCON, controls the different modes of operation of the PWM as well as the PWM
clock frequency. PWM0H/L and PWM1H/L are the data registers that determine the duty cycles. The output pins
that the PWM uses are determined by the CFG842 register, and can be either P2.6 and P2.7 or P3.4 and P3.3.
PWMCON: PWM Control Register
The output of sine generator is shows below
Output at DAC1
Pulse-Width Modulator (PWM)
8
SNGL MD2 MD1 MD0 CDIV1 CDIV0 CSEL1 CSEL0
Assembly Programming
SNGL: SET = Turns off PMW output at P2.6 or P3.4
MD2 MD1 MD0 Mode
0 0 0 PWM Disabled
0 0 1 Single variable resolution PWM on P2.7 or P3.3
0 1 0 Twin 8-bit PWM
0 1 1 Twin 16-bit PWM
1 0 0 Dual NRZ 16-bit ∑-∆ DAC
1 0 1 Dual 8-bit PWM
1 1 0 Dual RZ 16-bit ∑-∆ DAC
1 1 1 Reserved
CDIV1 CDIV0 Clock divider
0 0 Selected Clock/1
0 1 Selected Clock/4
1 0 Selected Clock/16
1 1 Selected Clock/64

11. To compute the values of 16-bit data registers PWM0H/L and PWM1H/L in mode 1:
Frequency: PWM1H/L = Fclk / Fdes
where: Fdes = Desired frequency (Hz)
Fclk = Frequency of clock source
Duty Cycle: PWM0H/L = Fclk / ((100/DC)*Fdes)
where: Fdes = Desired frequency (Hz)
Fclk = Frequency of clock source
DC = Duty Cycle
Example: Fdes = 1KHz; DC = 50%; Fclk = 16777216 Hz
PWM1H/L = 16777216 / 1000  16777  4189H  PWM1H = 41H, PWM1L = 89H
PWM0H/L = 16777216 / ((100/50)*1000)  8388  20C4H  PWM0H = 20H, PWM0L = C4H
Output at PWM1 (P2.7)
Assembly Programming
CSEL1 CSEL0 Clock Source
0 0 fXTAL/15
0 1 fXTAL
1 0 External input at P3.4/T0
1 1 fVCO = 16777216 Hz
9
Assembly Programming

12. ADC converts the analog input and provides an ADC 12-bit result word in the ADCDATAH/ADCDATAHL SFRs. The
top four bits of the ADCDATAH SFR are written with the channel selection bits to identify the channel result. The
ADC block provides the user with multichannel mux, track/hold, on-chip reference and calibration features.
ADCCON1: Controls conversion times and modes, and power-down
MD1 EXT_REF CK1 CK0 AQ1 AQ0 T2C EXC
ADCCON2: ADC channel selection and conversion modes
Analog to Digital Converter (ADC)
Assembly ProgrammingAssembly Programming
MD1: Cleared = Power down the ADC.
Set = Power on the ADC.
EXT_REF: Cleared = Internal reference (+2.5V).
Set = External reference (Vref pin).
CK1 CK0 ADC Clock (PLL clock divider, must be < 8.38 MHz)
0 0 32
0 1 4
1 0 8
1 1 2
A typical ADC conversion requires 16 ADC clocks plus the selected acquisition time.
AQ1 AQ0 Time for track-and-hold amplifier (ADC Clks, three or more is recommended)
0 0 1
0 1 2
1 0 3
1 1 4
T2C: Set = Enable the Timer 2 overflow bit to be used as the ADC conversion start trigger input.
EXC: Set = External Pin P3.5 (/CONVST) be used as the active low convert start input.
ADCI DMA CCONV SCONV CS3 CS2 CS1 CS0
ADCI (ADC Interrupt Bit): Set by hardware at the end of a single ADC conversion cycle.
Cleared by hardware when the PC vectors to the ADC interrupt service routine.
DMA (DMA Mode Enable Bit): Set = Enable a preconfigured ADC DMA mode operation.
CCONV (Continuous Conversion Bit): Set = Continuous Mode of Conversion.
SCONV (Single Conversion Bit): Set = Initiate a single conversion cycle. Is automatically reset to 0 on
completion of conversion cycle.
CS3, CS2, CS1, CS0 (ADC Channel Selection Bits): See User Manual.
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13. ADCCON3: ADC calibration modes and busy status
Buffering the analog inputs is a good for protection of analog input and implement antialiasing filter
Assembly Programming
BUSY 0 AVGS1 AVGS0 0 RSVD TYPICAL SCAL
BUSY (ADC Busy Status Bit): Set during ADC conversion or calibration cycle
AVGS1 AVGS0 ADC readings that are averaged during a calibration cycle
0 0 15
0 1 1
1 0 31
1 1 63
RSVD: Set by user when performing calibration.
TYPICAL: Set = Gain Calibration.
Clear = Offset Calibration
SCAL: Set = Start the selected calibration cycle
Cleared when the calibration cycle is completed
11

14. The following program shows how to implement the UART communication, was tested with Tera Term
UART Serial Interface
Assembly Programming
12

15. USB/UART Interface
Assembly Programming
13