TC7109/A
Figure through Figure give practical circuits utilizing
the parallel three-state output capabilities of the
TC7109A. Figure shows parallel interface to the 8748/
49 systems via an 8255 PPI, where the TC7109A data
outputs are active at all times. This interface can be
used in a read-after-update sequence, as shown in
Figure . The data is accessed by the high-to-low
transition of the Status driving an interrupt to the
microcontroller.
4.0
4.1
INTERFACING
Direct Mode
Combinations of chip enable and byte enable control
signals, which may be used when interfacing the
TC7109A to parallel data lines, are shown in Figure .
The CE/LOAD input may be tied low, allowing either byte
to be controlled by its own enable (see Figure (A)).
Figure (B) shows the HBEN and LBEN as flag inputs,
and CE/LOAD as a master enable, which could be the
READ strobe available from most microprocessors.
Figure (C) shows a configuration where the two byte
enables are connected together. The CE/LOAD is a
chip enable, and the HBEN and LBEN may be used as
a second chip enable, or connected to ground. The 14
data outputs will be enabled at the same time. In the
direct MODE, SEND should be tied to V+.
The RUN/HOLD input is also used to initiate
conversions under software control.
Direct interfacing to most microcontroller busses is
easily accomplished through the three-state output of
the TC7109A.
Figure 4-8 is a typical connection diagram. To ensure
requirements for setup and hold times, minimum pulse
widths, and the drive limitations on long busses are
met, it is necessary to carefully consider the system
timing in this type of interface. This type of interface is
used when the memory peripheral address density is
low, providing simple address decoding. Interrupt
handling can be simplified by using an interface to
reduce the component count.
Figure shows interfacing several TC7109A’s to a bus,
ganging the HBEN and LBEN signals to several
converters together, and using the CE/LOAD input to
select the desired converter.
Chip Select 1
Chip Select
GND
A. GND
B. GND
C.
MODE CE/LOAD
MODE
CE/LOAD
MODE CE/LOAD
B
- B
B - B
9 12
POL, OR
9
12
POL, OR
B
- B
12
POL, OR
6
6
1
14
TC7109A
B
TC7109A
B
TC7109A
- B
8
- B
8
8
1
8
1
Analog In
Analog In
Analog In
RUN/HOLD
LBEN
RUN/HOLD
LBEN
RUN/HOLD
LBEN
Convert
Convert
Convert
HBEN
HBEN
HBEN
GND or
Chip Select 2
Control
Byte Flags
FIGURE 4-1:
Direct Mode Chip and Byte Enable Combination
© 2006 Microchip Technology Inc.
DS21456C-page 17
MICROCHIP [ MICROCHIP ]
