AD822 datasheet(76/88 Pages) AD

76 / 88 page

ADuC841/ADuC842/ADuC843

Rev. 0 | Page 76 of 88

C1+

V+

C1–

C2+

C2–

V–

T2OUT

R2IN

VCC

GND

T1OUT

R1IN

R1OUT

T1IN

T2IN

R2OUT

ADM202

DVDD

9-PIN D-SUB

FEMALE

DVDD

Ω

DVDD

Ω

2-PIN HEADER FOR

EMULATION ACCESS

(NORMALLY OPEN)

DOWNLOAD/DEBUG

ENABLE JUMPER

(NORMALLY OPEN)

11.0592MHz (ADuC841)

32.768kHz (ADuC842/ADuC843)

DVDD

AVDD

AGND

CREF

VREF

DAC0

DAC1

DGND

DVDD

XTAL2

XTAL1

NOT CONNECTED IN THIS EXAMPLE

ADuC841/ADuC842/ADuC843

ADC0

ANALOG INPUT

VREF OUTPUT

DAC OUTPUT

Figure 85. Example System (PQFP Package), DACs Not Present on ADuC843

OTHER HARDWARE CONSIDERATIONS

To facilitate in-circuit programming, plus in-circuit debug and

emulation options, users will want to implement some simple

connection points in their hardware to allow easy access to

download, debug, and emulation modes.

In-Circuit Serial Download Access

Nearly all ADuC841/ADuC842/ADuC843 designs want to take

advantage of the in-circuit reprogrammability of the chip. This

is accomplished by a connection to the ADuC841/ADuC842/

ADuC843’s UART, which requires an external RS-232 chip for

level translation if downloading code from a PC. Basic configura-

tion of an RS-232 connection is illustrated in Figure 85 with a

simple ADM202 based circuit. If users would rather not design

an RS-232 chip onto a board, refer to Application Note uC006, A

4-Wire UART-to-PC Interface, (at www.analog.com/microconverter)

for a simple (and zero-cost-per-board) method of gaining in-

circuit serial download access to the part.

In addition to the basic UART connections, users also need a

way to trigger the chip into download mode. This is accom-

plished via a 1 kΩ pull-down resistor that can be jumpered onto

the PSEN pin, as shown in Figure 85. To get the part into download

mode, simply connect this jumper and power-cycle the device

(or manually reset the device, if a manual reset button is available),

and it will be ready to serially receive a new program. With the

jumper removed, the device comes up in normal mode (and

runs the program) whenever power is cycled or RESET is toggled.

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