LM3S6965 Microcontroller

Register 19: GPIO Lock (GPIOLOCK), offset 0x520

The GPIOLOCK register enables write access to the GPIOCR register (see page 204). Writing 0x1ACC.E551 to the GPIOLOCK register will unlock the GPIOCR register. Writing any other value to the GPIOLOCK register re-enables the locked state. Reading the GPIOLOCK register returns thelockstatusratherthanthe32-bitvaluethatwaspreviouslywritten.Therefore,whenwriteaccesses aredisabled,orlocked,readingthe GPIOLOCK registerreturns0x00000001. Whenwriteaccesses are enabled, or unlocked, reading the GPIOLOCK register returns 0x00000000.

GPIO Lock (GPIOLOCK)

GPIO Port A base: 0x4000.4000

GPIO Port B base: 0x4000.5000

GPIO Port C base: 0x4000.6000

GPIO Port D base: 0x4000.7000

GPIO Port E base: 0x4002.4000

GPIO Port F base: 0x4002.5000

GPIO Port G base: 0x4002.6000

Offset 0x520

Type R/W, reset 0x0000.0001

A write of any other value or a write to the GPIOCR register reapplies the lock, preventing any register updates. A read of this register returns the following values:

Value Description

0x0000.0001 locked

0x0000.0000 unlocked

Preliminary

General-Purpose Input/Outputs (GPIOs)

Register 20: GPIO Commit (GPIOCR), offset 0x524

The GPIOCR register is the commit register. The value of the GPIOCR register determines which bitsoftheGPIOAFSEL registerarecommittedwhenawritetotheGPIOAFSEL registerisperformed. If a bit in the GPIOCR register is a zero, the data being written to the corresponding bit in the GPIOAFSEL register will not be committed and will retain its previous value. If a bit in the GPIOCR register is a one, the data being written to the corresponding bit of the GPIOAFSEL register will be committed to the register and will reflect the new value.

The contents of the GPIOCR register can only be modified if the GPIOLOCK register is unlocked. Writes to the GPIOCR register are ignored if the GPIOLOCK register is locked.

Important: Thisregisterisdesignedtopreventaccidentalprogrammingoftheregistersthatcontrol connectivity to the JTAG/SWD debug hardware. By initializing the bits of the GPIOCR register to 0 for PB7 and PC[3:0], the JTAG/SWD debug port can only be converted to GPIOs through a deliberate set of writes to the GPIOLOCK, GPIOCR, and the corresponding registers.

Because this protection is currently only implemented on the JTAG/SWD pins on PB7 and PC[3:0], all of the other bits in the GPIOCR registers cannot be written with 0x0. These bits are hardwired to 0x1, ensuring that it is always possible to commit new values to the GPIOAFSELregister bits of these other pins.

GPIO Commit (GPIOCR)

GPIO Port A base: 0x4000.4000

GPIO Port B base: 0x4000.5000

GPIO Port C base: 0x4000.6000

GPIO Port D base: 0x4000.7000

GPIO Port E base: 0x4002.4000

GPIO Port F base: 0x4002.5000

GPIO Port G base: 0x4002.6000

Offset 0x524

Type -, reset -

Preliminary

LM3S6965 Microcontroller

GPIOs that are protected by the GPIOCR register. Because of this, the register type for GPIO Port B7 and GPIO Port C[3:0] is R/W.

The default reset value for the GPIOCR register is 0x0000.00FF for all GPIO pins, with the exception of the five JTAG/SWD pins (PB7 and PC[3:0]). To ensure that the JTAG port is not accidentally programmed as a GPIO, these five pins default to non-committable. Because of this, the default reset value of GPIOCR for GPIO Port B is 0x0000.007FwhilethedefaultresetvalueofGPIOCRforPort C is 0x0000.00F0.

Preliminary

General-Purpose Input/Outputs (GPIOs)

Register 21: GPIO Peripheral Identification 4 (GPIOPeriphID4), offset 0xFD0

The GPIOPeriphID4, GPIOPeriphID5, GPIOPeriphID6, and GPIOPeriphID7 registers can conceptuallybetreatedasone32-bitregister;eachregistercontainseightbitsofthe32-bitregister, used by software to identify the peripheral.

GPIO Peripheral Identification 4 (GPIOPeriphID4)

GPIO Port A base: 0x4000.4000

GPIO Port B base: 0x4000.5000

GPIO Port C base: 0x4000.6000

GPIO Port D base: 0x4000.7000

GPIO Port E base: 0x4002.4000

GPIO Port F base: 0x4002.5000

GPIO Port G base: 0x4002.6000

Offset 0xFD0

Type RO, reset 0x0000.0000

Preliminary