Datasheet

ATmega48/88/168 Automotive [DATASHEET]
7530K–AVR–07/14
6
2.3 Comparison Between ATmega48, ATmega88, and ATmega168
The Atmel
®
ATmega48, ATmega88 and ATmega168 differ only in memory sizes, boot loader support, and interrupt vector
sizes. Table 2-2 summarizes the different memory and interrupt vector sizes for the three devices.
ATmega88 and ATmega168 support a real read-while-write self-programming mechanism. There is a separate boot loader
section, and the SPM instruction can only execute from there. In ATmega48, there is no read-while-write support and no
separate boot loader section. The SPM instruction can execute from the entire flash.
2.4 Pin Descriptions
2.4.1 VCC
Digital supply voltage.
2.4.2 GND
Ground.
2.4.3 Port B (PB7..0) XTAL1/XTAL2/TOSC1/TOSC2
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The port B output buffers have
symmetrical drive characteristics with both high sink and source capability. As inputs, port B pins that are externally pulled
low will source current if the pull-up resistors are activated. The port B pins are tri-stated when a reset condition becomes
active, even if the clock is not running.
Depending on the clock selection fuse settings, PB6 can be used as input to the inverting oscillator amplifier and input to the
internal clock operating circuit.
Depending on the clock selection fuse settings, PB7 can be used as output from the inverting oscillator amplifier.
If the internal calibrated RC oscillator is used as chip clock source, PB7..6 is used as TOSC2..1 input for the asynchronous
Timer/Counter2 if the AS2 bit in ASSR is set.
The various special features of port B are elaborated in Section 10.3.2 “Alternate Functions of Port B” on page 64 and
Section 6. “System Clock and Clock Options” on page 23.
2.4.4 Port C (PC5..0)
Port C is a 7-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The PC5..0 output buffers have
symmetrical drive characteristics with both high sink and source capability. As inputs, Port C pins that are externally pulled
low will source current if the pull-up resistors are activated. The port C pins are tri-stated when a reset condition becomes
active, even if the clock is not running.
2.4.5 PC6/RESET
If the RSTDISBL Fuse is programmed, PC6 is used as an I/O pin. Note that the electrical characteristics of PC6 differ from
those of the other pins of Port C.
If the RSTDISBL fuse is unprogrammed, PC6 is used as a reset input. A low level on this pin for longer than the minimum
pulse length will generate a reset, even if the clock is not running. The minimum pulse length is given in Table 8-1 on page
40. Shorter pulses are not guaranteed to generate a reset.
The various special features of port C are elaborated in Section 10.3.3 “Alternate Functions of Port C” on page 67.
Table 2-2. Memory Size Summary
Device Flash EEPROM RAM Interrupt Vector Size
ATmega48 4Kbytes 256 Bytes 512 Bytes 1 instruction word/vector
ATmega88 8Kbytes 512 Bytes 1K Bytes 1 instruction word/vector
ATmega168 16Kbytes 512 Bytes 1K Bytes 2 instruction words/vector