Hardware and Software Constraints

SAM-BA Boot uses the first 2048 bytes of the SRAM for variables and stacks. The remaining available bytes can be used for the user code.

USB requirements:

External crystal or external clock (see Note below) with frequency of 12 MHz or 16 MHz

Note: Must be 2500 ppm and VDDIO square wave signal.

UART0 requirements:

None. If accurate external clock source is not available, the internal 12 MHz RC meets RS-232 standards at room temperature.

Table 1. Pins Driven during Boot Program Execution
Peripheral	Pin	PIO Line
UART0	URXD0	PA9
UART0	UTXD0	PA10