LM3S1918 Luminary Micro, Inc, LM3S1918 Datasheet - Page 54

• Manufacturer Part Number: LM3S1918
• Description: Lm3s1918 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

JTAG Interface
5.3
5.4
5.4.1
5.4.1.1
54
1.
2.
3.
Initialization and Configuration
After a Power-On-Reset or an external reset (RST), the JTAG pins are automatically configured for
JTAG communication. No user-defined initialization or configuration is needed. However, if the user
application changes these pins to their GPIO function, they must be configured back to their JTAG
functionality before JTAG communication can be restored. This is done by enabling the five JTAG
pins (PB7 and PC[3:0]) for their alternate function using the GPIOAFSEL register.
Register Descriptions
There are no APB-accessible registers in the JTAG TAP Controller or Shift Register chains. The
registers within the JTAG controller are all accessed serially through the TAP Controller. The registers
can be broken down into two main categories: Instruction Registers and Data Registers.
Instruction Register (IR)
The JTAG TAP Instruction Register (IR) is a four-bit serial scan chain with a parallel load register
connected between the JTAG TDI and TDO pins. When the TAP Controller is placed in the correct
states, bits can be shifted into the Instruction Register. Once these bits have been shifted into the
chain and updated, they are interpreted as the current instruction. The decode of the Instruction
Register bits is shown in Table 5-2 on page 54. A detailed explanation of each instruction, along
with its associated Data Register, follows.
Table 5-2. JTAG Instruction Register Commands
EXTEST Instruction
The EXTEST instruction does not have an associated Data Register chain. The EXTEST instruction
uses the data that has been preloaded into the Boundary Scan Data Register using the
SAMPLE/PRELOAD instruction. When the EXTEST instruction is present in the Instruction Register,
All Others
IR[3:0]
0000
0001
0010
1000
1010
1011
1110
1111
Send at least 50 TCK/SWCLK cycles with TMS/SWDIO set to 1. This ensures that both JTAG and
SWD are in their reset/idle states.
Send the 16-bit SWD-to-JTAG switch sequence, 16'hE73C.
Send at least 5 TCK/SWCLK cycles with TMS/SWDIO set to 1. This ensures that if SWJ-DP was
already in JTAG mode, before sending the switch sequence, the JTAG goes into the Test Logic
Reset state.
SAMPLE / PRELOAD
Instruction
Reserved
EXTEST
IDCODE
BYPASS
INTEST
ABORT
DPACC
APACC
Description
Drives the values preloaded into the Boundary Scan Chain by the SAMPLE/PRELOAD
instruction onto the pads.
Drives the values preloaded into the Boundary Scan Chain by the SAMPLE/PRELOAD
instruction into the controller.
Captures the current I/O values and shifts the sampled values out of the Boundary Scan
Chain while new preload data is shifted in.
Shifts data into the ARM Debug Port Abort Register.
Shifts data into and out of the ARM DP Access Register.
Shifts data into and out of the ARM AC Access Register.
Loads manufacturing information defined by the IEEE Standard 1149.1 into the IDCODE
chain and shifts it out.
Connects TDI to TDO through a single Shift Register chain.
Defaults to the BYPASS instruction to ensure that TDI is always connected to TDO.
Preliminary
July 26, 2008