3-44

TELCOM SEMICONDUCTOR, INC.

4

µsec 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

= 131msec.

(4) Calculate Load Value

tion and convert the resulting value to hexadeci-

mal:

256

fore, a LOAD VALUE of 10H is loaded to the TC520A. If the

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.

Figure 1. TC520A Initialization and Start/Stop Conversion Timing Relationships

LOAD

LOAD VALUE updated

and conversion started

TC520A CONVERSION STATE

CE is pulled

high only when

during AZ (DV = LOW)

New LOAD VALUE

can be loaded

(if so desired)

TC520A held in

AZ phase

as long as CE = HIGH

CE

AZ

INT

IZ

DINT

AZ

INT

INT

DINT

IZ

AZ

AZ

DV

LOAD VALUE

shifted into

LOAD

VALUE

TC520A

SERIAL INTERFACE ADAPTER FOR

TC500 A/D CONVERTER FAMILY