Rainbow Electronics АDC0805 - Manual (Page 30)

3D00 3E90 MVI 90
3D02 D3E7 Out Control Port Program PPI
3D04 2601 MVI H 01 Auto-Zero Subroutine
3D06 7C MOV A H
3D07 D3E6 OUT C Close SW1 open SW2
3D09 0680 MVI B 80 Initialize SAR bit pointer
3D0B 3E7F MVI A 7F Initialize SAR code
3D0D 4F MOV C A Return
3D0E D3E5 OUT B Port B 4 SAR code
3D10 31AA3D LXI SP 3DAA Start Dimension stack pointer
3D13 D3E4 OUT A Start A D
3D15 FB IE
3D16 00 NOP Loop Loop until INT asserted
3D17 C3163D JMP Loop
3D1A 7A MOV A D Auto-Zero
3D1B C600 ADI 00
3D1D CA2D3D JZ Set C Test A D output data for zero
3D20 78 MOV A B Shift B
3D21 F600 ORI 00 Clear carry
3D23 1F RAR Shift ‘1‘ in B right one place
3D24 FE00 CPI 00 Is B zero If yes last
3D26 CA373D JZ Done approximation has been made
3D29 47 MOV B A
3D2A C3333D JMP New C
3D2D 79 MOV A C Set C
3D2E B0 ORA B Set bit in C that is in same
3D2F 4F MOV C A position as ‘1‘ in B
3D30 C3203D JMP Shift B
3D33 A9 XRA C New C Clear bit in C that is in
3D34 C30D3D JMP Return same position as ‘1‘ in B
3D37 47 MOV B A Done then output new SAR code
3D38 7C MOV A H Open SW1 close SW2 then
3D39 EE03 XRI 03 proceed with program Preamp
3D3B D3E6 OUT C is now zeroed
3D3D Normal
Program for processing
proper data values
3C3D DBE4 IN A Read A D Subroutine Read A D data
3C3F EEFF XRI FF Invert data
3C41 57 MOV D A
3C42 78 MOV A B Is B Reg 4 0 If not stay
3C43 E6FF ANI FF in auto zero subroutine
3C45 C21A3D JNZ Auto-Zero
3C48 C33D3D JMP Normal
Note All numerical values are hexadecimal representations
FIGURE 20 Software for Auto-Zeroed Differential A D
5 3 Multiple A D Converters in a Z-80 Interrupt Driven
Mode (Continued)
The following notes apply
1) It is assumed that the CPU automatically performs a RST
7 instruction when a valid interrupt is acknowledged (CPU
is in interrupt mode 1) Hence the subroutine starting ad-
dress of X0038
2) The address bus from the Z-80 and the data bus to the Z-
80 are assumed to be inverted by bus drivers
3) A D data and identifying words will be stored in sequen-
tial memory locations starting at the arbitrarily chosen ad-
dress X 3E00
4) The stack pointer must be dimensioned in the main pro-
gram as the RST 7 instruction automatically pushes the
PC onto the stack and the subroutine uses an additional
6 stack addresses
5) The peripherals of concern are mapped into I O space
with the following port assignments
HEX PORT ADDRESS PERIPHERAL
00 MM74C374 8-bit flip-flop
01 A D 1
02 A D 2
03 A D 3
04 A D 4
05 A D 5
06 A D 6
07 A D 7
This port address also serves as the A D identifying word in
the program
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