The Silicon Laboratories C8051F020

The Silicon Laboratories C8051F020 Enhanced 8051 Part 2 Timers I ECE/CS-352: Embedded Microcontroller Systems

SFRs for Subsystems • Control registers: • XXXCN (WDTCN, ADC0CN, DAC0CN, TMR3CN) • Configuration registers: • XXXCF (ADC0CF, AMX0CF, EMI0CF) • Data registers for subsystems: • ADC0H, ADC0L, DAC0H, DAC0L • Many others..... ECE/CS-352: Embedded Microcontroller Systems

System Clocks • Internal clock oscillator • default at reset • 2 MHz default frequency • configured by SFR OSCICN • External oscillator installed on board • 22.1184 MHz • configured by SFR OSCXCN ECE/CS-352: Embedded Microcontroller Systems

Internal Osc ConfigurationOSCICN Missing clock detector enable Internal Osc. frequency ready Internal Osc. freq. control bits 00 – 2MHz 01 – 4 MHz 10 – 8 MHz 11 – 16 MHz system clock select 0 = internal 1 = external (internal by default) Default Sysclk f = 2 MHz T = ?? Internal Osc. enable (enabled by default) ECE/CS-352: Embedded Microcontroller Systems

External Osc. ConfigurationOSCXCN • External Osc. freq. control bits • Depends on frequency range of operation External Osc. mode bits 00x: Off. XTAL1 pin is grounded internally. 010: System Clock from External CMOS Clock on XTAL1 pin. 011: System Clock from External CMOS Clock on XTAL1 pin divided by 2. 10x: RC/C Oscillator Mode with divide by 2 stage. 110: Crystal Oscillator Mode 111: Crystal Oscillator Mode with divide by 2 stage. Crystal Osc. valid flag ECE/CS-352: Embedded Microcontroller Systems

Development Board Oscillator ECE/CS-352: Embedded Microcontroller Systems

To use 22.1184 MHz external oscillator 110: Crystal Oscillator Mode 111: f > 6.7 MHz Step 1. Configure the external oscillator. Step 2. Wait at least 1 ms. Step 3. Poll for XTLVLD => ‘1’. Step 4. Switch the system clock to the external oscillator. ECE/CS-352: Embedded Microcontroller Systems

Instruction Timing • C8051F020 – Pipelined architecture • Machine cycle = clock cycle • Most instructions take 1 or 2 clock cycles • Total of 109 distinct instruction types • Summary of instruction timing: ECE/CS-352: Embedded Microcontroller Systems

Delay Loops clr A djnz A, $ ; 2 cycles if no jump, ; 3 cycles if jump ECE/CS-352: Embedded Microcontroller Systems

Sample Configuration • Use 22.1184 MHzexternal oscillator Main: mov WDTCN, #0deh ; disable watchdog timer mov WDTCN, #0adh mov OSCXCN, #67h ; enable external crystal ; oscillator at 22.1184MHz clr A ; wait at least 1ms djnz A, $ ; wait ~510us (255 x 4 x 0.5us) = 510 us) djnz A, $ ; wait ~510us osc_wait: ; poll for XTLVLD-->1 mov a, OSCXCN jnb acc.7, osc_wait orl OSCICN, #08h ; select external oscillator as ; system clock source ECE/CS-352: Embedded Microcontroller Systems

Timers • Original 8051 has 2 Timers, T0 and T1 • Can think of timers as binary counters • Clock is derived from system clock (frequency is configurable) • Timer registers can be read via mov instructions • Events (interrupts or flag bits set) occur when timers overflow • Can be used to create waveforms, measure time intervals, set frequency of events, etc. ECE/CS-352: Embedded Microcontroller Systems

C8051F020 Timers Size of timers can be configured. • Timers can count from arbitrary initial value with the “Auto-reload” feature. • “Capture” allows the timer to be “frozen” when an event occurs. • Timers 2 and 4 can be used to set baud rate for uarts. ECE/CS-352: Embedded Microcontroller Systems

Timer Clock Sources CKCON: Clock Control Register Timer0 Timer clock selects 0 = system clock  12 (for compatibility with original 8051, and for slow stuff) 1 = system clock Timer4 ECE/CS-352: Embedded Microcontroller Systems

Configuring Timers • TCON and TMOD used to configure Timer0 and Timer1 TCON: Timer Control Register These deal with external interrupts Timer 1 Overflow Flag Timer 1 run control 0 = disable Timer 1 1 = enable Timer 1 ECE/CS-352: Embedded Microcontroller Systems

Configuring Timers TMOD: Timer Mode Register Timer 1 Timer 0 GATE1: 0 = timer enabled with TR1 only 1 = timer enabled only when TR1=1 and \INT=1 C/T1: 0 = timer incremented by clock input 1 = counter incremented by edge on external T1 pin ECE/CS-352: Embedded Microcontroller Systems

Using Timers For Periodic EventsUsing Polling • Set mode to be timer – use appropriate clock and timer size • In main program • Check for overflow flag (polling) • When overflow flag occurs • Do event • Reset timer overflow flag • Reset timer initial value (unless using auto-reload or initial value of 0 is OK) • Continue checking ECE/CS-352: Embedded Microcontroller Systems

Using Timers For Periodic EventsUsing Interrupts • Set mode to be timer, use appropriate clock and timer size • Set timer to interrupt on overflow • In Interrupt Service Routine • Do event • Reset interrupt flag • Reset timer to initial value (unless using auto-reload) • Return from interrupt ECE/CS-352: Embedded Microcontroller Systems

Using Timers as Counter • Set mode to be counter, with appropriate size (8, 13 or 16 bits) • Initialize counter to zero • Enable counter • Counter can be read and reset by main program. ECE/CS-352: Embedded Microcontroller Systems

Using Timers to Measure Time Using Timers: • Configure timers with mode 0 or 1 (13 or 16-bit timer) and desired system clock. • In main program, wait for initial event. • Start the timer. • Each time the timer overflows, a register should be incremented using an interrupt service routine. • When the second event occurs, disable the interrupts and the timer in the main program. ECE/CS-352: Embedded Microcontroller Systems

Configuration Tool • Fortunately, there is a tool to help configure all the subsystems in the 8051. • This makes things a lot easier. • To access the tool, go to Silicon Labs – Configuration Tool 2 ECE/CS-352: Embedded Microcontroller Systems

The Silicon Laboratories C8051F020