Introduction to Virtual I2C Bus Serial Display Circuit

　　1. SAA1064 pin function

　　① VDD, VEE: power supply, ground terminal. Power supply 4.5～15V;

　　② P1～P16: Segment drive output terminal. Divided into two 8-bit ports:

　　P1～P8;P9～P16. P8 and P16 are high. The port latch has an inverting function. When it is set to 1, the port outputs 0.

　　③ MX1, MX2: Bit code drive end. In static display drive, one SAA1064 can drive a two-digit LED digital tube; in dynamic display drive, according to the connection method in Figure 9-10, one SAA1064 can drive a four-digit LED digital tube;

　　④ SDA, SCL: I2C bus data terminal, clock terminal;

　　⑤ CEXT: Clock oscillator external capacitor, typical value 2700pF

　　⑥ ADR: address pin. SAA1064 pin addresses A1 and A0 are addressed using ADR analog voltage comparison. When the ADR pin level is 0, 3VDD/8, 5VDD/8, VDD, the corresponding pin addresses A2, A1, A0 are 000, 001, 010, 011 respectively;

　　2. Hardware circuit design

3. On-chip programmable functions
       

　　CO: static and dynamic control, C0=1, dynamic display, when dynamic display, data1 and data2 are output from P8~P1 in turn, and data3 and data4 are output from P16~P9 in turn;

　　C1: Display position 1, 3 light or dark selection, C1=1, select light;

　　C2: Display position 2, 4 light or dark selection, C2=1, select light;

　　C3: test bit, C3=1, all segments are on;

　　C4, C5, C6: drive current control bits. When C4, C5, C6 are 1 respectively, the drive current is 3mA, 6mA, 12mA respectively. When C4, C5, C6 are all 1, the drive current is the maximum, which can reach 21mA.

　　⑶ Write data operation format
       

　　The red part is sent by 80C51 and received by SAA1064; the black part is sent by SAA1064 and received by 80C51.

　　SLAW is the addressing byte for writing SAA1064.

　　Connect the circuit as shown in the figure: SAA1064 (1) SLAW = 01110000B; SAA1064 (2) SLAW = 01110110B. Among them, 0111 (D7~4) is the SAA1064 device address, D3~1 is the A2A1A0 addressing byte, the last bit D0 is R/W; SADR is the on-chip register address; COM is the control command.

4. Programming

　　Example: Given that the 8-bit display symbol (common negative code) has been stored in RAM 51H to 58H in sequence, try to program it according to Figure 9-10 and input it into SAA1064 (1), (2) for dynamic display, with a drive current of 12mA. Assume that the VIIC software package has been loaded into ROM, and VSDA.VSCL.SLA.NUMB.MTD.MRD have all been defined according to the protocol in 8.3.2 Software Package Summary.

　　VSAA: MOV MTD, #00H; Set the SAA1064 control command register COM chip sub-address

　　            MOV 31H, #01000111B; set control command word, dynamic display, drive current 12mA

　　           MOV NUMB,#6; Set the number of data to be sent: SADR+COM+data1～4=6

　　SAA1: MOV RO,#51H ; Move the display data from 51H to 54H to 32H to 35H

　　           LCALL MOVB ;

　　           MOV SLA,#01110000B; Set SAA1064(1) to write the addressing byte SLAW

　　           LCALL WRNB ; send to SAA1064 (1)

　　SAA2: MOV R0,#55H ; Move the display character data from 55H to 58H to 32H to 35H

　　           LCALL MOVB ;

　　           MOV SLA,#01110110B; Set SAA1064 (2) address byte SLAW

　　           LCALL WRNB ; send to SAA1064 (2)

　　           RET ;

　　MOVB: MOV R1,#32H ; Display character data is moved to 32H～35H subroutine

　　MOVB1:MOV A,@R0 ; read

　　           MOV @R1,A ; store

　　           INC RO; points to the next read unit

　　           INC R1 ; point to the next storage unit

　　           CJNE R1,#36H,MOVB1; Check if the 4 data have been moved. If not, continue.

　　           RET ;