LM3S6938 Luminary Micro, Inc, LM3S6938 Datasheet - Page 34

• Manufacturer Part Number: LM3S6938
• Description: Lm3s6938 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

Architectural Overview
1.4.6
1.4.6.1
1.4.6.2
1.4.7
1.4.7.1
1.4.7.2
34
The Watchdog Timer can be configured to generate an interrupt to the controller on its first time-out,
and to generate a reset signal on its second time-out. Once the Watchdog Timer has been configured,
the lock register can be written to prevent the timer configuration from being inadvertently altered.
Memory Peripherals
The LM3S6938 controller offers both single-cycle SRAM and single-cycle Flash memory.
SRAM (see page 142)
The LM3S6938 static random access memory (SRAM) controller supports 64 KB SRAM. The internal
SRAM of the Stellaris
reduce the number of time-consuming read-modify-write (RMW) operations, ARM has introduced
bit-banding technology in the new Cortex-M3 processor. With a bit-band-enabled processor, certain
regions in the memory map (SRAM and peripheral space) can use address aliases to access
individual bits in a single, atomic operation.
Flash (see page 143)
The LM3S6938 Flash controller supports 256 KB of flash memory. The flash is organized as a set
of 1-KB blocks that can be individually erased. Erasing a block causes the entire contents of the
block to be reset to all 1s. These blocks are paired into a set of 2-KB blocks that can be individually
protected. The blocks can be marked as read-only or execute-only, providing different levels of code
protection. Read-only blocks cannot be erased or programmed, protecting the contents of those
blocks from being modified. Execute-only blocks cannot be erased or programmed, and can only
be read by the controller instruction fetch mechanism, protecting the contents of those blocks from
being read by either the controller or by a debugger.
Additional Features
Memory Map (see page 42)
A memory map lists the location of instructions and data in memory. The memory map for the
LM3S6938 controller can be found in “Memory Map” on page 42. Register addresses are given as
a hexadecimal increment, relative to the module's base address as shown in the memory map.
The ARM® Cortex™-M3 Technical Reference Manual provides further information on the memory
map.
JTAG TAP Controller (see page 47)
The Joint Test Action Group (JTAG) port is an IEEE standard that defines a Test Access Port and
Boundary Scan Architecture for digital integrated circuits and provides a standardized serial interface
for controlling the associated test logic. The TAP, Instruction Register (IR), and Data Registers (DR)
can be used to test the interconnections of assembled printed circuit boards and obtain manufacturing
information on the components. The JTAG Port also provides a means of accessing and controlling
design-for-test features such as I/O pin observation and control, scan testing, and debugging.
The JTAG port is composed of the standard five pins: TRST, TCK, TMS, TDI, and TDO. Data is
transmitted serially into the controller on TDI and out of the controller on TDO. The interpretation of
this data is dependent on the current state of the TAP controller. For detailed information on the
operation of the JTAG port and TAP controller, please refer to the IEEE Standard 1149.1-Test
Access Port and Boundary-Scan Architecture.
The Luminary Micro JTAG controller works with the ARM JTAG controller built into the Cortex-M3
core. This is implemented by multiplexing the TDO outputs from both JTAG controllers. ARM JTAG
instructions select the ARM TDO output while Luminary Micro JTAG instructions select the Luminary
®
devices is located at offset 0x0000.0000 of the device memory map. To
Preliminary
July 25, 2008