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The 8-KB SRAM maps to the DATA memory space and to parts of the XDATA memory spaces. The SRAM is
an ultralow-power SRAM that retains its contents even when the digital part is powered off (power modes 2
The 128/256 KB flash block provides in-circuit programmable non-volatile program memory for the device,
and maps into the CODE and XDATA memory spaces.
Writing to the flash block is performed through a flash controller that allows page-wise erasure and 4-bytewise
A versatile five-channel DMA controller is available in the system, accesses memory using the XDATA
memory space, and thus has access to all physical memories. Each channel (trigger, priority, transfer mode,
addressing mode, source and destination pointers, and transfer count) is configured with DMA descriptors that
can be located anywhere in memory. Many of the hardware peripherals (AES core, flash controller, USARTs,
timers, ADC interface, etc.) can be used with the DMA controller for efficient operation by performing data
transfers between a single SFR or XREG address and flash/SRAM.
Each CC2540 contains a unique 48-bit IEEE address that can be used as the public device address for a
Bluetooth device. Designers are free to use this address, or provide their own, as described in the Bluetooth
The interrupt controller services a total of 18 interrupt sources, divided into six interrupt groups, each of which
is associated with one of four interrupt priorities. I/O and sleep timer interrupt requests are serviced even if the
device is in a sleep mode (power modes 1 and 2) by bringing the CC2540 back to the active mode.
The debug interface implements a proprietary two-wire serial interface that is used for in-circuit debugging.
Through this debug interface, it is possible to erase or program the entire flash memory, control which
oscillators are enabled, stop and start execution of the user program, execute instructions on the 8051 core,
set code breakpoints, and single-step through instructions in the code. Using these techniques, it is possible
to perform in-circuit debugging and external flash programming elegantly.
The I/O controller is responsible for all general-purpose I/O pins. The CPU can configure whether peripheral
modules control certain pins or whether they are under software control, and if so, whether each pin is
configured as an input or output and if a pullup or pulldown resistor in the pad is connected. Each peripheral
that connects to the I/O pins can choose between two different I/O pin locations to ensure flexibility in various
The sleep timer is an ultra low power timer that uses an external 32.768-kHz crystal oscillator. The sleep timer
runs continuously in all operating modes except power mode 3. Typical applications of this timer are as a real-
time counter or as a wake-up timer to exit power modes 1 or 2.
A built-in watchdog timer allows the CC2540 to reset itself if the firmware hangs. When enabled by software,
the watchdog timer must be cleared periodically; otherwise, it resets the device when it times out.
Timer 1 is a 16-bit timer with timer/counter/PWM functionality. It has a programmable prescaler, a 16-bit
period value, and five individually programmable counter/capture channels, each with a 16-bit compare value.
Each of the counter/capture channels can be used as a PWM output or to capture the timing of edges on input
signals. It can also be configured in IR generation mode, where it counts timer 3 periods and the output is
ANDed with the output of timer 3 to generate modulated consumer IR signals with minimal CPU interaction.
Timer 2 is a 40-bit timer used by the Bluetooth low energy stack. It has a 16-bit counter with a configurable
timer period and a 24-bit overflow counter that can be used to keep track of the number of periods that have
transpired. A 40-bit capture register is also used to record the exact time at which a start-of-frame delimiter is
received/transmitted or the exact time at which transmission ends. There are two 16-bit timer-compare
registers and two 24-bit overflow-compare registers that can be used to give exact timing for start of RX or TX
to the radio or general interrupts.
Timer 3 and timer 4 are 8-bit timers with timer/counter/PWM functionality. They have a programmable
prescaler, an 8-bit period value, and one programmable counter channel with an 8-bit compare value. Each of
the counter channels can be used as PWM output.