AT89LP216-20PI datasheet(63/90 Pages) ATMEL

63 / 90 page

3621A–MICRO–6/06

AT89LP216 [Preliminary]

22. On-Chip Debug System

The AT89LP216 On-Chip Debug (OCD) System uses a two-wire serial interface to control pro-

gram flow; read, modify, and write the system state; and program the nonvolatile memory. The

OCD System has the following features:

• Complete program flow control

• Read-Modify-Write access to all internal SFRs and data memories

• Four hardware program address breakpoints

• Unlimited program software breakpoints using BREAK instruction

• Break on stack overflow/underflow

• Break on Watchdog overflow

• Non-intrusive operation

• Programming of nonvolatile memory

22.1

Physical Interface

The On-Chip Debug System uses a two-wire synchronous serial interface to establish communi-

cation between the target device and the controlling emulator system. The OCD interface is

controlled by two User Fuses. OCD is enabled by clearing the OCD Enable Fuse. When OCD is

enabled, the RST port pin is configured as an input for the Debug Clock (DCL). Either the XTAL1

or XTAL2 pin is configured as a bi-directional data line for the Debug Data (DDA) depending on

the clock source selected. If the External Clock is selected, XTAL2 is configured as DDA. If the

Internal RC Oscillator is selected, XTAL1 is configured as DDA. The OCD device connections

are shown in Figure 22-1. When OCD is enabled, the type of interface used depends on the

OCD Interface Select User Fuse. This fuse selects between a normal two-wire interface (TWI)

and a fast two-wire interface (FTWI). It is the duty of the user to program this fuse to the correct

setting for their debug system at the same time they enable OCD (see “User Configuration

Fuses” on page 71).

Figure 22-1. AT89LP216 On-Chip Debug Connections

When designing a system where On-Chip Debug will be used, the following observations must

be considered for correct operation:

• P1.3/RST cannot be connected directly to V

CC and any external capacitors connect to RST

must be removed.

• All external reset sources must be removed.

• The quartz crystal and any capacitors on XTAL1 or XTAL2 must be removed and an external

clock signal must be driven on XTAL1 if the user does not wish to use the internal RC

oscillator. Some emulator systems may provide a user-configurable clock for this purpose.

CLK = Internal RC

VCC

XTAL1

P1.3/RST

GND

DCL

DDA

CLK = External Clock

VCC

XTAL2

P1.3/RST

GND

DCL

DDA

XTAL1

CLK

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