HI-7159A データシートの表示（PDF） - Intersil
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HI-7159A Datasheet PDF : 14 Pages
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HI-7159A
SEND COMMAND BYTE
(INITIATE SINGLE CONVERSION)
GET STATUS BYTE
NO
D6 = 1?
YES
GET DIGIT BYTES
CONVERSION RESULT
IS VALID
FIGURE 5. READING THE HI-7159A IN THE SINGLE
CONVERSION MODE
GET STATUS BYTE
NO
D6 = 1?
YES
GET DIGIT BYTES
GET STATUS BYTE
CONVERSION
RESULT IS
VALID
YES
NO
D6 = 0?
CONVERSION
RESULT MAY
BE INVALID:
DISCARD
RESULT
FIGURE 6. READING THE HI-7159A IN THE CONTINUOUS
CONVERSION MODE
Due to the wide range of baud rates available in the serial
modes, some of the lower baud rates will take longer to transfer
the output data than it takes to perform a conversion. In these
cases the continuous mode should not be used. Table 11
shows the percentage of the total conversion time that it takes
to read all the data from the converter for the two serial modes.
These are best case numbers, assuming that the bytes are
transmitted and received end-to-end. An asterisk indicates that
it is impossible to get all the data out within one conversion.
Percentages in the 20-50% range indicate that it is possible to
get valid data out with very tight code. In all cases the status
byte should be checked before and after the reading to ensure
data integrity.
BAUD
RATE
300
1200
9600
TABLE 11. SERIAL MODES 1/2
51/2 COMP
*/*
54%/*
7%/13%
CONVERSION TYPE
51/2
UNCOMP
*/*
41/2 COMP
*/*
*/*
*/*
14%/25% 27%/50%
41/2
UNCOMP
*/*
*/*
54%/*
19200
4%/7% 7%/13% 14%/25% 27%/50%
Crystal Oscillator
The HI-7159A uses a single pin crystal oscillator design
(Figure 7). The crystal is connected between Pin 27 and
VCC; no load capacitors or other components are
necessary. The user has a choice of crystal frequencies:
2.4576MHz or 2.4MHz. An off-the-shelf 2.4576MHz crystal
works well and provides baud rates of exactly 19.2K, 9600,
1200, and 300. However its total integration period will be
16.28ms, or 0.39ms shorter than a 60Hz cycle. This
effectively reduces the normal mode AC rejection.
+5V
VCC
1
CRYSTAL
(2MHz TO 2.5MHz)
HI-7159A 27
XTAL
FIGURE 7. SINGLE-PIN OSCILLATOR
A 2.4MHz crystal results in an integration period of 16.67ms,
exactly the length of one 60Hz AC cycle. Normal mode AC
rejection is greatest at this frequency. At 2.4MHz, however,
the Baud rates will be off by -2.34%. This error is not large
enough to cause any errors with most peripherals, and only
applies to operation in Serial Modes 1 and 2.
Communication in Serial Mode 0 and the Parallel Mode is
independent of the crystal frequency. For this mode a
2.4MHz crystal is recommended.
While the oscillator was designed to operate at
2MHz - 2.5MHz, the HI-7159A itself will operate reliably
down to less than 600kHz when driven with an external
clock. Benefits at lower clock frequencies include reduced
rollover error (gain error for negative input voltages) and
lower noise. The baud rates mentioned throughout this data
sheet correspond to a crystal frequency of 2.4576MHz. At
1.2MHz, the actual baud rates will be half the speed they
were at 2.4MHz, i.e., 9600, 4800, 600 and 150 baud. At
600kHz they will be one-fourth.
10
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