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Pin Descriptions
VCC
GND
Port B (PB7..PB0)
Port D (PD6..PD0)
RESET
XTAL1
XTAL2
Crystal Oscillator
0838H–AVR–03/02
ing the Registers, Timer/Counter, Watchdog and Interrupt system to continue
functioning. The Power-down mode saves the register contents but freezes the Oscilla-
tor, disabling all other chip functions until the next External Interrupt or hardware Reset.
The device is manufactured using Atmel's high-density nonvolatile memory technology.
The On-chip In-System Programmable Flash allows the program memory to be repro-
grammed in-system through an SPI serial interface or by a conventional nonvolatile
memory programmer. By combining an enhanced RISC 8-bit CPU with In-System Pro-
grammable Flash on a monolithic chip, the Atmel AT90S1200 is a powerful
microcontroller that provides a highly flexible and cost-effective solution to many embed-
ded control applications.
The AT90S1200 AVR is supported with a full suite of program and system development
tools including: macro assemblers, program debugger/simulators, in-circuit emulators,
and evaluation kits.
Supply voltage pin.
Ground pin.
Port B is an 8-bit bi-directional I/O port. Port pins can provide internal pull-up resistors
(selected for each bit). PB0 and PB1 also serve as the positive input (AIN0) and the
negative input (AIN1), respectively, of the On-chip Analog Comparator. The Port B out-
put buffers can sink 20 mA and thus drive LED displays directly. When pins PB0 to PB7
are used as inputs and are externally pulled low, they will source current if the internal
pull-up resistors are activated. The Port B pins are tri-stated when a reset condition
becomes active, even if the clock is not active.
Port B also serves the functions of various special features of the AT90S1200 as listed
on page 30.
Port D has seven bi-directional I/O pins with internal pull-up resistors, PD6..PD0. The
Port D output buffers can sink 20 mA. As inputs, Port D pins that are externally pulled
low will source current if the pull-up resistors are activated. The Port D pins are tri-stated
when a reset condition becomes active, even if the clock is not active.
Port D also serves the functions of various special features of the AT90S1200 as listed
on page 34.
Reset input. A low level on this pin for more than 50 ns will generate a reset, even if the
clock is not running. Shorter pulses are not guaranteed to generate a reset.
Input to the inverting oscillator amplifier and input to the internal clock operating circuit.
Output from the inverting oscillator amplifier.
XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can
be configured for use as an On-chip Oscillator, as shown in Figure 2 . Either a quartz
crystal or a ceramic resonator may be used. To drive the device from an external clock
source, XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 3.
AT90S1200
3
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