Microprocessor and Interfacing 261313

Microprocessor and Interfacing261214PIC Code Execution IIhttp://mango.e-cpe.org

PICB0

B1

B2

B3

B4

B5

B6

B7

Memory Mapped I/O (MMIO)BSF06.0BCF06.0BSF = Bit Set File, BCF = Bit Clear File Memory Mapped I/O I/O

MOVWF 06MOVWF 21I/O OperationMem Operation

Memory Mapped I/OMemory Mapped I/O Memory CPU

Memory MappedPort-MappedWith some exceptions Memory Mapped I/O Memory PIC16F886 128 Byte 368 Bytes (~35%) Memory Mapped I/O

128 BytesI/O Mapped240 BytesAvailable RAM

3.x GB?? 4 GBThe 3 Gig RAM Problem32 bit OSInstalledUsable 32 RAM 2^32 = 4GB 3.x GB

The 3 Gig RAM Problem~1 GB3 GB

Address SpaceVideo CardBIOSPCI BusEtc.RAM(4 GB) I/O

Memory Mapped I/O Memory I/O data bus Memory Access I/O

MOVWF 06MOVWF 21Slow I/O OperationFastMem Operation

Port Mapped I/O (PMIO)Memory Operation Peripheral Operation CPU Port Mapped I/O Memory Mapped I/O / Port Mapped I/O CPU

PIC 16FIntel x8635 Instructions1,000+ Instructions** See http://en.wikipedia.org/wiki/X86_instruction_listingsMemory Mapped I/O Case StudyPIC 16F, Tri-state I/O, Memory OrganizationLook at the complete ASM code foroutput_high(PIN_B0).................... output_high(PIN_B0); 00ED: BSF 03.500EE: BCF 06.000EF: BCF 03.500F0: BSF 06.0Q: Why do we need these commands?A: Before using a PIN on the PIC, we need to configure its direction

Each MCU PIN can be in 3 states (Tri-State)StateDescriptionHighThe pin sources 5VLowThe pin sinks to GNDHigh ImpedanceThe pin is an inputOutputModeInputModeTri-state PIN configurationTelling the MCU which mode we want to use an IO pin

0 = Output1 = Input.................... output_high(PIN_B0); 00EE: BCF 86.0 -> Clear bit 0 of TRISB00F0: BSF 06.0 -> Set bit 0 of PORTB.................... output_high(PIN_B0); 00ED: BSF 03.500EE: BCF 06.000EF: BCF 03.500F0: BSF 06.0So, the code should be like this But why is it like this?The problem with BCF 86.0

0x86 = 1000 0110The space for the file register address is limited to 7 bitsStatus Register (Address 03)

See section Register 5-1 in the handoutfor details of the Status RegisterBit 6,7 Register Bank

00 = Bank 001 = Bank 110 = Bank 211 = Bank 3

Bank 0Bank 1Bank 2Bank 3 PIC Simulator IDE; set PORTB as outputbsf status,5bcf status,6movlw 0movwf trisb; disable Analog inputsbsf status,6movwf 0x189; switch to FSR Bank 0bcf status,5bcf status,6bsf portb,0 ; trun on LED on B0 setup The RLF commandRotates the bits in a file register through the carry bit

RLFExample:MOVLW1MOVWF0x6 ; RAM value = 0000 00012RLF 0x6,F ; value is now 0000 00102Status Register (Address 03)

Zero Bit = 1 ALU 0

See section Register 5-1 in the handoutfor details of the Status RegisterPIC-C Trick: RAM access#byte b_port = 6 // mem pointer#bit B0 = b_port.0

b_port = 0xff; // drive port bB0 = 1; // set bit B0 to 1

Machine Code Generation MethodsMethodsWrite Machine Code ManuallyWrite Assembly CodeUse a High-Level Compiler

Writing Machine CodeENIAC

Benefits of High-Level CompilersPoor optimizationNon-Optimal Hardware UtilizationDrawbacks of High-Level CompilersSimple for the programmerReduce development timeAllows for the development of larger programsEasier to port to different hardware systemsPoor Optimazation.................... while (1) .................... output_b(i); Loop:BSF 03.5CLRF 06BCF 03.5MOVF 21,WMOVWF 06GOTO LoopNo need to set TRIS bits every timePoor Optimization Ex 2.................... int i; .................... i = 5; 000D: MOVLW 05000E: BCF 03.5000F: MOVWF 21.................... do { .................... i--; 0010: DECF 21,F.................... } while (i>0); 0011: MOVF 21,F0012: BTFSS 03.2 0013: GOTO 010 DECF already sets the Z bitNon-Optimal HW UtilizationBlinking LED exampleOur code from exercise BSF06.0Loop: RLF06 GoTo Loop

Code generated by PIC-CLoop: BCF 03.5 MOVF 0x21,W MOVWF 06 RLF 0x21, F GOTO Loop