HI-7159A Ver la hoja de datos (PDF) - Renesas Electronics
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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
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.
TABLE 11. SERIAL MODES 1/2
BAUD
RATE
300
1200
9600
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
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-
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.
FN2936 Rev 4.00
January 1999
Page 10 of 14
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