DDC232_15 Datasheet, PDF (15/34 Pages) Texas Instruments – 32-Channel, Current-Input Analog-to-Digital Converter

DDC232
www.ti.com
SBAS331D – AUGUST 2004 – REVISED APRIL 2010
Continuous and Noncontinuous Operational
Modes
Figure 10 shows the state diagram of the DDC232. In
all, there are eight states. Table 8 provides a brief
explanation of each state.
CONV|mbsy
1
CONV • mbsy
Ncont
2
Ncont
CONV • mbsy
CONV
3
Int A
Cont
CONV
4
Int B/Meas A
Cont
CONV • mbsy
CONV • mbsy
5
Int A/Meas B
Cont
CONV
6
Int B
Cont
CONV
CONV • mbsy
7
Ncont
CONV • mbsy
8
Ncont
CONV|mbsy
State Diagram Notation:
CONV • mbsy = CONV high AND mbsy active.
CONV|mbsy = CONV high OR mbsy active.
Figure 10. Integrate/Measure State Diagram
Four signals are used to control progression around
the state diagram: CONV, mbsy, and their
complements. The state machine uses the level as
opposed to the edges of CONV to control the
progression. mbsy is an internally-generated signal
not available to the user. It is active whenever a
measurement/reset/auto-zero (m/r/az) cycle is in
progress.
During the Continuous (Cont) mode, mbsy is not
active when CONV toggles. The nonintegrating side
is always ready to begin integrating when the other
side finishes its integration. Consequently, monitoring
the current status of CONV is all that is needed to
know the current state. Cont mode operation
corresponds to states 3 to 6. Two of the states, 3 and
6, only perform an integration (that is, no m/r/az
cycle).
mbsy becomes important when operating in the
Noncontinuous (Ncont) mode (states 1, 2, 7, and 8).
Whenever CONV is toggled while mbsy is active, the
DDC232 will enter or remain in either Ncont state 1
(or 8). After mbsy goes inactive, state 2 (or 7) is
entered. This state prepares the appropriate side for
integration. In the Ncont states, the inputs to the
DDC232 are grounded.
One interesting observation from the state diagram is
that the integrations always alternate between sides
A and B. This relationship holds for any CONV
pattern and is independent of the mode. States 2 and
7 ensure this relationship during the Ncont mode.
When power is first applied to the DDC232, the
beginning state is either 1 or 8, depending on the
initial level of CONV. For CONV held high at
power-up, the beginning state is 1. Conversely, for
CONV held low at power-up, the beginning state is 8.
In general, there is a symmetry in the state diagram
between states 1–8, 2–7, 3–6, and 4–5. Inverting
CONV results in the states progressing through their
symmetrical match.
STATE
1
2
3
4
5
6
7
8
MODE
Ncont
Ncont
Cont
Cont
Cont
Cont
Ncont
Ncont
Table 8. State Descriptions
DESCRIPTION
Complete m/r/az of side A, then side B (if previous state is state 4). Initial power-up state
when CONV is initially held high.
Prepare side A for integration.
Integrate on side A.
Integrate on side B; m/r/az on side A.
Integrate on side A; m/r/az on side B.
Integrate on side B.
Prepare side B for integration.
Complete m/r/az of side B, then side A (if previous state is state 5). Initial power-up state
when CONV is initially held low.
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Product Folder Link(s): DDC232
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