Analog Devices ADuC812 manual Other Hardware Considerations, In-Circuit Serial Download Access

ADuC812

DOWNLOAD/DEBUG

ENABLE JUMPER

(NORMALLY OPEN)

DVDD

1k

DV

DD

1k

2-PIN HEADER FOR

EMULATION ACCESS

52

51

50

49 48

47 46

45 44 43

42 41

40

(NORMALLY OPEN)

51

DV

DGND

PSEN

EA

ANALOG INPUT

ADC0

DD

39

38

37

AVDD

36

DVDD

AVDD

DGND 35

AGND

ADuC812

DVDD 34

VREF OUTPUT

CREF

XTAL2 33

11.0592MHz

VREF

XTAL1 32

DAC0

31

DAC1

30

DAC OUTPUT

ADC7

RESET

RxD

TxD

DV

DGND

29

DD

28

27

DVDD

ADM810

NOT CONNECTED IN THIS EXAMPLE

VCC

RST

DVDD

GND
ADM202		DVDD	9-PIN D-SUB
C1+	VCC		FEMALE
V+	GND		1
C1–	T1OUT		2
C2+	R1IN		3
C2–	R1OUT		4
V–	T1IN		5
T2OUT	T2IN		6
R2IN	R2OUT		7
			8
			9

Figure 46. Typical System Configuration

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 that will allow easy access to download, debug, and emulation modes.

In-Circuit Serial Download Access

Nearly all ADuC812 designs will want to take advantage of the in-circuit reprogrammability of the chip. This is accomplished by a connection to the ADuC812’s UART, which requires an external RS-232 chip for level translation if downloading code from a PC. Basic configuration of an RS-232 connection is illustrated in Figure 46 with a simple ADM202-based circuit. If users would rather not design an RS-232 chip onto a board, refer to the applica- tion note “uC006–A 4-Wire UART-to-PC Interface”* for a simple (and zero-cost-per-board) method of gaining in-circuit serial download access to the ADuC812.

In addition to the basic UART connections, users will 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

*Application Note uC006 is available at www.analog.com/microconverter

the PSEN pin, as shown in Figure 46. To get the ADuC812 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 receive a new program serially. With the jumper removed, the device will come up in normal mode (and run the program) whenever power is cycled or RESET is toggled.

Note that PSEN is normally an output (as described in the External Memory Interface section) and it is sampled as an input only on the falling edge of RESET (i.e., at power-up or upon an external manual reset). Note also that if any external circuitry unintentionally pulls PSEN low during power-up or reset events, it could cause the chip to enter download mode and therefore fail to begin user code execution as it should. To pre- vent this, ensure that no external signals are capable of pulling the PSEN pin low, except for the external PSEN jumper itself.

Embedded Serial Port Debugger

From a hardware perspective, entry to serial port debug mode is identical to the serial download entry sequence described above. In fact, both serial download and serial port debug modes can be thought of as essentially one mode of operation used in two different ways.

–44– REV. B