TC850CLW View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
TC850CLW Datasheet PDF : 26 Pages
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TC850
6.0 DIGITAL SECTION
DESCRIPTION
The TC850 digital section consists of two sets of con-
version counters, control and sequencing logic, clock
oscillator and divider, data latches and an 8-bit, 3-state
interface bus. A simplified schematic of the bus
interface logic is shown in Figure 6-1
6.1 Clock Oscillator
The TC850 includes a crystal oscillator on-chip. All that
is required is to connect a crystal across OSC1 and
OSC2 pins and to add two inexpensive capacitors
(Figure 1-1). The oscillator output is ÷ 4 prior to clock-
ing the A/D internal counters. For example, a 100 kHz
crystal produces a system clock frequency of 25 kHz.
Since each conversion requires 1280 clock periods, in
this case the conversion rate will be 25,000/1280, or
19.5 conversions per second.
In most applications, however, an external clock is
divided down from the microprocessor clock. In this
case, the OSC1 pin is used as the external oscillator
input and OSC2 is left unconnected. The external clock
driver should swing from digital ground to VDD. The ÷ 4
function is active for both external clock and crystal
oscillator operations.
DBO–DB7
L/H
RD
CE
CS
POL/OVR
3-State
8
Octal
8
Buffer
8 2-Input Mux
7
Output
Enable
Select
Low-Byte
Up/Down
Counter
High-Byte
Up/Down
Counter
TC850
Select
2-Input Mux
Polarity
To A/D
Control Logic
WR
CONT/
DEMAND
Start
Conversion
Overrange
FIGURE 6-1:
End of Conversion
Bus Interface Simplified Schematic
6.2 Digital Operating Modes
Two modes of operation are available with the TC850,
continuous conversions and on-demand. The Operat-
ing mode is controlled by the CONT/DEMAND input.
The bus interface method is different for Continuous
and Demand modes of operation.
6.2.1 DEMAND MODE OPERATION
When CONT/DEMAND is low, the TC850 performs one
conversion each time the chip is selected and the WR
input is pulsed low. Data is valid on the falling edge of
the BUSY output and can be accessed using the
interface truth table (Table 6-1).
6.2.2 CONTINUOUS MODE OPERATION
When CONT/DEMAND is high, the TC850 continu-
ously performs conversions. Data will be valid on the
falling edge of the BUSY output and remains valid for
443-1/2 clock cycles.
The low/high (L/H) byte-select and overrange/polarity
(OVR/POL) inputs are disabled during Continuous mode
operation. Data must be read in three consecutive bytes,
as shown in Table 6-1.
Note:
In Continuous mode, the conversion result
must be read within 443-1/2 clock cycles
of the BUSY output falling edge. After this
time (i.e.,1/2 clock cycle before BUSY
goes high) the internal counters are reset
and the data is lost.
DS21479C-page 12
© 2006 Microchip Technology Inc.
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