TC520A Datasheet, PDF (6/8 Pages) TelCom Semiconductor, Inc – SERIAL INTERFACE ADAPTER FOR TC500 A/D CONVERTER FAMILY

SERIAL INTERFACE ADAPTER FOR
TC500 A/D CONVERTER FAMILY
TC520A
4µsec makes the SYSCLK frequency equal to
250kHz. This makes the external crystal (or fre-
quency source) equal to 1.0MHz (since SYSCLK =
crystal frequency/4). Calculating integration time (in
msec) using T_SYSCLK = 4µsec, T_INT = µsec x 32768
= 131msec.
(4) Calculate Load Value
Plug the T_INT and T_SYSCLK values into the equa-
tion and convert the resulting value to hexadeci-
mal:
LOAD VALUE = [(65536 - (T_INT/T_SYSCLK)]
256
In this example, LOAD VALUE = 128₍₁₀₎ = 10H. There-
fore, a LOAD VALUE of 10H is loaded to the TC520A. If the
desired T_INT was 100msec instead of 131msec, the LOAD
VALUE would be 9EH, and so on. The TC520A LOAD
VALUE must be initialized on power-up, and can be re-
initialized as often as desired thereafter. This is accom-
plished by bringing the LOAD input low while transmitting the
appropriate LOAD VALUE to the TC520A as shown in
Figure 1 and Figure 2.
Polled vs. Interrupt Operation
The TC520A can be accessed at any time by the host
microprocessor. This makes operation in a polled environ-
ment especially easy since the most recently converted data
is available to the processor as needed. The TC520A can
also be used in an interrupt environment by connecting DV
to the IRQ line of the processor. Since AZ is the first phase
of a new conversion cycle, the most recently converted data
will be available as soon as DV goes low. If so desired, the
interrupt service routine can also modify the LOAD VALUE
during the DV = low interval.
Opto-Isolated Applications
The 3 wire serial port of the TC520A can be opto-
isolated for applications requiring isolated data acquisition.
The additional control lines (LOAD, DV, READ) are normally
not needed in such applications, but can also be brought
across the isolation barrier with the addition of a second
isolator.
LOAD
CE
D_IN, D_CLK
DV
AZ INT
DINT
TC520A CONVERSION STATE
IZ AZ INT
DINT
IZ
AZ
CE is pulled
high only when
during AZ (DV = LOW)
AZ
INT
LOAD VALUE updated
and conversion started
LOAD VALUE
shifted into
D_IN
New LOAD VALUE
can be loaded
(if so desired)
LOAD
VALUE
TC520A held in
AZ phase
as long as CE = HIGH
Figure 1. TC520A Initialization and Start/Stop Conversion Timing Relationships
3-44
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