ADC0804LCWM datasheet(21/56 Pages) TI1

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ADC0801, ADC0802, ADC0803, ADC0804, ADC0805

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SNOSBI1C – NOVEMBER 2009 – REVISED JUNE 2015

Figure 30. Mapping the ADC as an I/O Device for Use With the Z-80 CPU

Additional I/O advantages exist as software DMA routines are available and use can be made of the output data

transfer which exists on the upper 8 address lines (A8 to A15) during I/O input instructions. For example, MUX

channel selection for the ADC can be accomplished with this operating mode.

9.1.2.5 Interfacing 6800 Microprocessor Derivatives (6502, etc.)

The control bus for the 6800 microprocessor derivatives does not use the RD and WR strobe signals. Instead it

employs a single R/W line and additional timing, if needed, can be derived from the

φ2 clock. All I/O devices are

memory mapped in the 6800 system, and a special signal, VMA, indicates that the current address is valid.

Figure 36 shows an interface schematic where the ADC is memory mapped in the 6800 system. For simplicity,

the CS decoding is shown using 1/2 DM8092. Note in many 6800 systems, an already decoded 4/5 line is

brought out to the common bus at pin 21. This can be tied directly to the CS pin of the ADC, provided that no

other devices are addressed at HX ADDR: 4XXX or 5XXX.

The following subroutine performs essentially the same function as in the case of the 8080A interface and it can

be called from anywhere in the user’s program.

In Figure 38 the ADC0801 series is interfaced to the M6800 microprocessor through (the arbitrarily chosen) Port

B of the MC6820 or MC6821 Peripheral Interface Adapter, (PIA).

Here the CS pin of the ADC is grounded because the PIA is already memory mapped in the M6800 system and

no CS decoding is necessary. Also notice that the ADC output data lines are connected to the microprocessor

bus under program control through the PIA and therefore the ADC RD pin can be grounded.

A sample interface program equivalent to the previous one is shown below Figure 38. The PIA Data and Control

Registers of Port B are located at HEX addresses 8006 and 8007, respectively.

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