214 CHAPTER 5 Working with J-Link and J-Trace
J-Link / J-Trace (UM08001) ©
2004-2017 SEGGER Microcontroller GmbH & Co. KG
Legend
• RO: Variable is read-only
• WO: Variable is write-only
• R/W: Variable is read-write
Variable Description R/W
CPU
Pre-selects target CPU J-Link is communicating
with. Used in InitTarget() to skip the core auto-
detection of J-Link. This variable can only be set
to a known global J-Link DLL constant. For a list
of all valid values, please refer to Global DLL con-
stants on page 217.
Example
CPU = ARM926EJS;
WO
JTAG_IRPre
Used for JTAG chain configuration. Sets the num-
ber of IR-bits of all devices which are closer to
TDO than the one we want to communicate with.
Example
JTAG_IRPre = 6;
R/W
JTAG_DRPre
Used for JTAG chain configuration. Sets the num-
ber of devices which are closer to TDO than the
one we want to communicate with.
Example
JTAG_DRPre = 2;
RO
JTAG_IRPost
Used for JTAG chain configuration. Sets the num-
ber of IR-bits of all devices which are closer to
TDI than the one we want to communicate with.
Example
JTAG_IRPost = 6;
RO
JTAG_DRPost
Used for JTAG chain configuration. Sets the num-
ber of devices which are closer to TDI than the
one we want to "communicate with.
Example
JTAG_DRPost = 0;
RO
JTAG_IRLen
IR-Len (in bits) of the device we want to commu-
nicate with.
Example
JTAG_IRLen = 4;
RO
JTAG_TotalIRLen
Computed automatically, based on the values of
JTAG_IRPre, JTAG_DRPre, JTAG_IRPost and
JTAG_DRPost.
Example
v = JTAG_TotalIRLen;
RO
JTAG_AllowTAPReset
En-/Disables auto-JTAG-detection of J-Link. Has
to be disabled for devices which need some spe-
cial init (for example to add the core to the JTAG
chain), which is lost at a TAP reset.
Allowed values
0 Auto-detection is enabled.
1 Auto-detection is disabled.
WO
JTAG_Speed
Sets the JTAG interface speed. Speed is given in
kHz.
Example
JTAG_Speed = 2000; // 2MHz JTAG speed
R/W
Table 5.11: Global DLL variables
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