Microprocessor and Interfacing 261214. PIC Flash Memory Segments 2K 01012.

งานนำเสนอเรื่อง: "Microprocessor and Interfacing 261214. PIC Flash Memory Segments 2K 01012."— ใบสำเนางานนำเสนอ:

1 Microprocessor and Interfacing 261214

2 PIC Flash Memory Segments 2K 01012

3 PIC’s RAM Banking

4 Instruction Format

5 f = 7 bit Maximum memory = 2^7 = 128 Bytes

6 PIC 16F877 has 512 bytes of RAM: How do we access all of it? STATUS (F# 0x03) Bit 5-6 (RP0,RP1) in STATUS are used for RAM Page selection 07 Total Memory becomes 2^9 = 512 Bytes

7 Creating a 9 bit RAM address STATUS 07 068 f (File#) 06713 9 Bit RAM Address OPCODE

8 void main() { int i; i = 1; i++; }.................... int i;........................................ i=1; 000D: MOVLW 01 000E: BCF 03.5 000F: MOVWF 21.................... i++; 0010: INCF 21,F This code should now make sense

9 RAM location First 32 bytes of every page are reserved. Except on pages 3 and 4 User RAM space. Last 16 Bytes are mirrored

10 The big picture: where the bits are Bit 5-6 (RP0,RP1) in STATUS are used for RAM Page selection 07 Bit 3-4 in PCLATH are used for memory access 07 4 3 6 5

11 2. เร่ง Memory Operations ด้วย Indirect Addressing

12 ทำไมต้องมี Indirect Addressing? สมมุติว่าเรามี Array ในภาษา C ดังนี้ int value[8]; หลังจากที่ใช้งานมันไปสักพักเราอยาก Clear ค่าใน array ทั้งหมดมีค่าเป็น 0 Code จะเป็นอย่างไรถ้าเราไม่สามารถใช้ตัวแปรอ้างตำแหน่ง ใน Array เช่นห้ามใช้ value[i] = 0;

13 With indirect addressing For (i=0 ; i<8 ; i++) { value[i] = 0; } Without indirect addressing Value[0] = 0; Value[1] = 0; Value[2] = 0; Value[3] = 0; Value[4] = 0; Value[5] = 0; Value[6] = 0; Value[7] = 0;

14 PIC’s Indirect Addressing OpcodeFile

15 Creating a 9 bit indirect RAM address STATUS 07 078 8-bit address 07 9 Bit RAM Address FSR (File #4)

16

17 Example: clear RAM locations 0x20 – 0x27 (8 Bytes) InstructionComment BCF0x03, 7 ;select page MOVLW0x20 MOVWF0x04 ;Set FSR NextCLRF0x00 ;clear RAM INCFFSR,F ;increase counter BTFSSFSR,3 ;all done? GOTONext ; no, clear next 0x20 = 0b0010 0000 0x27 = 0b0010 0111

18 The big picture: where the bits are Bit 5-6 (RP0,RP1) in STATUS are used for RAM Page selection 07 Bit 3-4 in PCLATH are used for memory access 07 4 3 6 5 Bit 7 (IRP) in STATUS is used for indirect Addressing

19 Indirect Addressing Ex Find the sum of values in RAM address 0x22-0x25 and store at address 0x21 AddressFunction 0x21Sum 0x22Value1 0x23Value2 0x24Value3 0x25Value4 End Result: Sum = Value1+Value2+Value3+Value4 ; 0x21 = sum result variable clrf0x21 ; 0x22 - 0x25 = input numbers to be summed movlw4 movwf0x22 movlw3 movwf0x23 movlw2 movwf 0x24 movlw1 movwf0x25