AT43USB326-AU Atmel, AT43USB326-AU Datasheet - Page 21

• Manufacturer Part Number: AT43USB326-AU
• Description: IC USB KEYBOARD CTRLR 48LQFP
• Manufacturer: Atmel
• Series: AVR®r

Specifications of AT43USB326-AU

• Applications: Keyboard Controller
• Core Processor: AVR
• Program Memory Type: Mask ROM (16 kB)
• Controller Series: AT43USB
• Ram Size: 512 x 8
• Interface: USB
• Number Of I /o: 32
• Voltage - Supply: 4.4 V ~ 5.25 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Figure 6. Reset Logic
Power-on Reset
3313D–USB–04/06
System Clock
RSTN
VCC
Watchdog Timer
When the USB hardware is reset, the compound device is de-configured and has to be re-
enumerated by the host. When the microcontroller is reset, all I/O registers are then set to their
initial values, and the program starts execution from address $000. The instruction placed in
address $000 must be a JMP instruction to the reset handling routine. If the program never
enables an interrupt source, the interrupt vectors are not used, and regular program code can
be placed at these locations. The circuit diagram in Figure 6 shows the reset logic. The user
can select the start-up time according to typical oscillator start-up. The number of WDT oscilla-
tor cycles used for each time-out is shown in Table 7.
Table 7. Number of Watchdog Oscillator Cycles
A Power-on Reset (POR) circuit ensures that the device is reset from power-on. An internal
timer clocked from the Watchdog timer oscillator prevents the MCU from starting until after a
certain period after V
rise time.
If the build-in start-up delay is sufficient, RESET can be connected to V
external pull-up resistor. By holding the pin low for a period after V
Power-on Reset period can be extended.
Reset Ckt
POR Ckt
FSTRT
Programmed
Unprogrammed
Divider
CC
USB Reset
has reached the power-on threshold voltage, regardless of the V
14-bit Cntr
Time-out at V
1.1 ms
16.0 ms
OR
CC
= 5V
Cntr Reset
FSTRT
Number of WDT cycles
1K
16K
AT43USB326
CC
R
has been applied, the
S
CC
directly or via an
ON
21
CC