AT90S4414
OC1B
Pin Descriptions
VCC
OC1B is the output pin for the Timer/Counter1 Output
CompareB function
Supply voltage
GND
ALE
ALE is the Address Latch Enable used when the External
Memory is enabled. The ALE strobe is used to latch the
low-order address (8 bits) into an address latch during the
first access cycle, and the AD0-7 pins are used for data
during the second access cycle.
Ground
Port A (PA7..PA0)
Port A is an 8-bit bidirectional I/O port. Port pins can pro-
vide internal pull-up resistors (selected for each bit). The
Port A output buffers can sink 20mA and can drive LED dis-
plays directly. When pins PA0 to PA7 are used as inputs
and are externally pulled low, they will source current if the
internal pull-up resistors are activated.
Crystal Oscillator
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.
Port A serves as Multiplexed Address/Data input/output
when using external SRAM.
Port B (PB7..PB0)
Port B is an 8-bit bidirectional I/O pins with internal pull-up
resistors. The Port B output buffers can sink 20 mA. As
inputs, Port B pins that are externally pulled low will source
current if the pull-up resistors are activated.
Figure 2. Oscillator Connections
Port B also serves the functions of various special features
of the AT90S4414 as listed on page 45.
Port C (PC7..PC0)
Port C is an 8-bit bidirectional I/O port with internal pull-up
resistors. The Port C output buffers can sink 20 mA. As
inputs, Port C pins that are externally pulled low will source
current if the pull-up resistors are activated.
Port C also serves as Address output when using external
SRAM.
Port D (PD7..PD0)
Port D is an 8-bit bidirectional I/O port with internal pull-up
resistors. 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.
Figure 3. External Clock Drive Configuration
Port D also serves the functions of various special features
of the AT90S4414 as listed on page 51.
RESET
Reset input. A low on this pin for two machine cycles while
the oscillator is running resets the device.
XTAL1
Input to the inverting oscillator amplifier and input to the
internal clock operating circuit.
XTAL2
Output from the inverting oscillator amplifier
ICP
ICP is the input pin for the Timer/Counter1 Input Capture
function.
3
ATMEL [ ATMEL ]
