6
AT43USB324
1941A–02/01
Signal Description
Signal
Type
Name and Functions
VCC
V
Power Supply
– 5V supply input
CEXT
O
External Capacitor
– A high quality 0.47 µF must be connected to CEXT for proper
operation of the chip.
VSS
V
Ground
XTAL1
I
Oscillator Input
– Input to the inverting oscillator amplifier
XTAL2
O
Oscillator Output
– Output of the inverting oscillator amplifier
LFT
I
PLL Filter
– For proper operation of the PLL, this pin should be connected through
a 0.01 µF capacitor in parallel with a 100
Ω
resistor in series with a 0.22 µF
capacitor to ground (VSS). Both capacitors must be high quality ceramic
DP0
U
Upstream Plus USB I/O
– This pin should be connected to CEXT1 through an
external 1.5 k
Ω
pull-up resistor. DP0 and DM0 form the differential signal pin pairs
connected to the host controller or an upstream hub
DM0
U
Upstream Minus USB I/O
DP[2,3]
U
Port Plus USB I/O
– Each of these pins should be connected to VSS through an
external 15 k
Ω
resistor. The DP[2,3] and DM[2,3] are the differential signal-pin pairs
to connect downstream USB devices
DM[2,3]
U
Port Minus USB I/O
– Each of these pins should be connected to VSS through an
external 15 k
Ω
resistor
PA[0:7]
B
Port A[0:7]
– Bi-directional 8-bit I/O port with controlled slew rate. These pins are
used as eight of the keyboard matrix column output strobes: PA[0:7] = COL[0:7]
PB[0:7]
B
Port B[0:7]
– Bi-directional 8-bit I/O port with controlled slew rate. These pins are
used as the eight of the keyboard matrix column output strobes: PB[0:7] =
COL[8:15]
PC[0:7]
B
Port C[0:7]
– Bi-directional 8-bit I/O port with internal pull-ups. These pins are used
as keyboard matrix row input signals: PC[0:7] = ROW[0:7]
PD[0:7]
B
Port D[0:7]
– Bi-directional I/O ports. PD[4:7] have built-in series limiting resistors
and can be used to drive LEDs directly. An alternate function of PD2 is as INT0 and
PD3 is as INT1, the external interrupt pins
PE[0:1]
B
Port E[0:1]
– Bi-directional I/O port with controlled slew rate which can be used as
two additional keyboard column output strobes: COL 16, 17
RESET
I
Reset
– A low on this pin for two machine cycles while the oscillator is running
resets the device
TEST
I
Test Pin
– This pin should be tied to ground
