 2000 Infineon Technologies Corp. • Optoelectronics Division • San Jose, CA

www.infineon.com/opto • 1-888-Infineon (1-888-463-4636)

OSRAM Opto Semiconductors GmbH & Co. OHG • Regensburg, Germany

www.osram-os.com • +49-941-202-7178

1

May 31, 2000-14

This application note introduces the user to one of the features

of Timer 2 and A/D converter of the SAB 80515/535. Included in

this application note is a description of both the software and

hardware implementations of the SAS 80515/535 to use its

Timer 2 and 8-bit A/D converter for the bidirectional, speed reg-

ulated moving message display. The program listing demon-

strates how the Timer 2 and the 8-bit A/D converter of the SAB

80515/535 can be combined to generate time delays controlled

by analog levels. The hardware circuitry shows an interface of

the SAP 80515/535 with a simulated analog input, a 2 kbyte

EPROM, and intelligent display chips of Siemens used in mem-

ory mapped 1/0 scheme.

The SAB 80515/535 microcontroller with on-chip A/D converter

and a 16-bit Timer (Timer 2) with reload capability offers a solution

which can be applied to a wide range of industrial applications.

These applications vary from analog controlled digital delays to

controlled frequency converters for pulse width modulation.

In the present application example, the above features of the

SAB 80515/535 are used in conjunction to generate the soft-

ware delays. The software delay results in varying the voltage

level of the analog signal applied to the A/D converter of the

SAB 80515/535.

A/D Converter

The SAB 80515/535 provides an 8-bit A/D converter with eight

multiplexed analog input channels on-chip. In addition, the A/D

converter has a sample and hold circuit and offers the feature

of software programmable reference voltages. For the conver-

sion, the method of successive approximation with a capacitor

network is used.

Figure 1 shows a block diagram of the A/D converter. There are

three user-accessible special function registers:

—ADCON (A/D converter control register)

—ADDAT (A/D converter data register)

—DAPR (D/A converter program register) for the programma-

ble reference voltages.

Special function register ADCON is used to select one of the

eight analog input channels to be converted, to specify a single

or continuous conversion, and to check the status bit BSY

which signals whether a conversion is in progress or not.

The special function register ADDAT holds the converted digital

8-bit data result. The data remains in ADDAT until it is overwrit-

ten by the next converted data. The new converted value will

appear in ADDAT in the 15th machine cycle after a conversion

has been started. ADDAT can be read and written to under soft-

ware control. If the A/D converter of the SAB 80515/535 is not

used, register ADDAT can be used as an additional general-pur-

pose register.

The special function register DAPR is provided for program-

ming the internal reference voltages IVAREF and IVAGND. In

the present application DAPR holds a value of 00H. For this

value of DAPR, IVAREF and IVAGND are the same as VAREF

and VAGND respectively.

A/D Conversion

A conversion is started by writing to the special function regis-

ter DAPR. A “Write-to-DAPR” will start a new conversion even

if a conversion is currently in progress. The conversion begins

with the next machine cycle. The busy flag BSY will be set in

the same machine cycle as the “write-to-DAPR” operation

occurs. If the value written to DAPR is 00H, meaning that no

adjustment of the internal reference voltages is desired, the

conversion needs 15 machine cycles to be completed. Thus,

the conversion time is 15 µs for 12 MHz oscillator frequency.

After a conversion has been started by writing into the special

function register DAPR, the analog voltage at the selected input

channel is sampled for 5 machine cycles (5 µs at 12 MHz oscil-

lator frequency), which will then be held at the sampled level

for the rest of the conversion time.

The external analog source must be strong enough to source

the current in order to load the sample & hold capacitance,

being 25 pF, within those 5 machine cycles.

Interfacing the PD243X

SAB80515/SAB80535 Microcontroller

To Produce a Bidirectional, Speed Regulated

Moving Message Display by Using the SAB80515/SAB80535's Timer 2 & 8-Bit

Converter

Appnote 49