MC145053 Motorola, MC145053 Datasheet - Page 6

• Manufacturer Part Number: MC145053
• Description: 10-Bit A/D Converter a Serial Interface
• Manufacturer: Motorola

DIGITAL INPUTS AND OUTPUT
are illustrated in the timing diagrams of Figures 9 through 14.
Table 1 assists in selection of the appropriate diagram. Note
that the ADC accepts 16 clocks which makes it SPI (Serial
Peripheral Interface) compatible.
CS
Active-Low Chip Select Input (Pin 10)
provides 3-state control of the data output pin (D out ). While
inactive high, CS forces D out to the high-impedance state
and disables the data input (D in ) and serial clock (SCLK)
pins. A high-to-low transition on CS resets the serial data
port and synchronizes it to the MPU data stream. CS can re-
main active during the conversion cycle and can stay in the
active low state for multiple serial transfers or CS can be in-
active high after each transfer. If CS is kept active low be-
tween transfers, the length of each transfer is limited to either
10 or 16 SCLK cycles. If CS is in the inactive high state be-
tween transfers, each transfer can be anywhere from 10 to
16 SCLK cycles long. See the SCLK pin description for a
more detailed discussion of these requirements.
mized by the internal circuitry. Any transitions on the CS pin
are recognized as valid only if the level is maintained for
about 2 s after the transition.
No. of Clocks in
MC145053
6
Serial Transfer
The various serial bit-stream formats for the MC145053
Chip select initializes the chip to perform conversions and
Spurious chip selects caused by system noise are mini-
11 to 16
11 to 16
If CS is inactive high after the 10th SCLK cycle
and then goes active low before the A/D conver-
sion is complete, the conversion is aborted and
the chip enters the initial state, ready for another
serial transfer/conversion sequence. At this point,
the output data register contains the result from
the conversion before the aborted conversion.
Note that the last step of the A/D conversion se-
quence is to update the output data register with
the result. Therefore, if CS goes active low in an
attempt to abort the conversion too close to the
end of the conversion sequence, the result regis-
ter may be corrupted and the chip could be thrown
out of sync with the processor until CS is toggled
again (refer to the AC Electrical Characteristics in
the spec tables).
10
10
16
16
Table 1. Timing Diagram Selection
PIN DESCRIPTIONS
Using
Yes
Yes
Yes
CS
No
No
No
Don’t Care
Don’t Care
Shorter than Conversion
Shorter than Conversion
Longer than Conversion
Longer than Conversion
NOTE
Serial Transfer
Interval
Figure
No.
10
11
12
13
14
9
D out
Serial Data Output of the A/D Conversion Result
(Pin 11)
active high. When the chip recognizes a valid active low on
CS, D out is taken out of the high-impedance state and is driv-
en with the MSB of the previous conversion result. (For the
first transfer after power-up, data on D out is undefined for the
entire transfer.) The value on D out changes to the second
most significant result bit upon the first falling edge of SCLK.
The remaining result bits are shifted out in order, with the
LSB appearing on D out upon the ninth falling edge of SCLK.
Note that the order of the transfer is MSB to LSB. Upon the
10th falling edge of SCLK, D out is immediately driven low (if
allowed by CS) so that transfers of more than 10 SCLKs read
zeroes as the unused LSBs.
en from a low level to the MSB of the conversion result for
three cases: Case 1 — upon the 16th SCLK falling edge if
the transfer is longer than the conversion time (Figure 14);
Case 2 — upon completion of a conversion for a 16-bit trans-
fer interval shorter than the conversion (Figure 12); Case 3
— upon completion of a conversion for a 10-bit transfer (Fig-
ure 10).
D in
Serial Data Input (Pin 12)
analog mux address (or the user test mode) that is to be con-
verted next. The address is shifted in on the first four rising
edges of SCLK. After the four mux address bits have been
received, the data on D in is ignored for the remainder of the
present serial transfer. See Table 2 in Applications In-
formation.
SCLK
Serial Data Clock (Pin 13)
perform three major functions: (1) drives the data shift regis-
ters to simultaneously shift in the next mux address from the
D in pin and shift out the previous conversion result on the
D out pin, (2) begins sampling the analog voltage onto the RC
DAC as soon as the new mux address is available, and (3)
transfers control to the A/D conversion state machine after
the last bit of the previous conversion result has been shifted
out on the D out pin.
ing SCLK rates down to the dc. There are some cases, how-
ever, that require a minimum SCLK frequency as discussed
later in this section. At least ten SCLK cycles are required for
each simultaneous data transfer. If the 16-bit format is used,
SCLK can be one continuous 16-bit stream or two intermit-
tent 8-bit streams. After the serial port has been initiated to
perform a serial transfer*, the new mux address is shifted in
* The serial port can be initiated in three ways: (1) a recognized CS
falling edge, (2) the end of an A/D conversion if the port is perform-
ing either a 10-bit or a 16-bit “shorter-than-conversion” transfer
with CS active low between transfers, and (3) the 16th falling edge
of SCLK if the port is performing 16-bit “longer-than-conversion”
transfers with CS active low between transfers.
This output is in the high-impedance state when CS is in-
When CS is held active low between transfers, D out is driv-
The four-bit serial input stream begins with the MSB of the
This clock input drives the internal I/O state machine to
The serial data shift registers are completely static, allow-
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