VSC8601 Datasheet
Functional Descriptions
SAMPLE/PRELOAD Allows a snapshot of inputs and outputs during normal system
operation to be taken and examined. It also allows data values to be loaded into the
boundary-scan cells prior to the selection of other boundary-scan test instructions.
IDCODE Provides the version number (bits 31:28), part number (bits 27:12), and the
manufacturer identity (bits 11:1) to be serially read from the device.
The following table provides information about the meaning of IDCODE binary values
stored in the device JTAG registers.
Table 4.
JTAG Device Identification Register Description
Device Version
Number
Manufacturing
Identity
Description
Bit field
Model Number
LSB
0
31 through 28
0001
27 through 12
11 through 1
Binary value
1000 0110 0000 0001 000 0111 0100
1
CLAMP Allows the state of the signals driven from the component pins to be
determined from the boundary-scan register while the bypass register is selected as the
serial path between TDI and TDO. While the CLAMP instruction is selected, the signals
driven from the component pins do not change.
HIGHZ Places the component in a state in which all of its system logic outputs are
placed in a high impedance state. In this state, an in-circuit test system may drive
signals onto the connections normally driven by a component output without incurring a
risk of damage to the component. This makes it possible to use a board where not all of
the components are compatible with the IEEE 1149.1 standard.
BYPASS The bypass register contains a single shift-register stage and is used to
provide a minimum-length serial path (one TCK clock period) between TDI and TDO to
bypass the device when no test operation is required.
The following table provides more information about the location and IEEE compliance
of the JTAG instruction codes used in the VSC8601.
Table 5.
JTAG Interface Instruction Codes
Register
Width
IEEE 1149.1
Specification
Instruction
EXTEST
Code
0000
0001
0110
0010
0011
1111
Selected Register
Boundary-scan
45
45
32
1
Mandatory
Mandatory
Optional
SAMPLE/PRELOAD
IDCODE
Boundary-scan
Device identification
Bypass register
Bypass register
Bypass register
CLAMP
Optional
HIGHZ
1
Optional
BYPASS
1
Mandatory
RESERVED
0100, 0101,
0111, 1000-1110
Revision 4.1
September 2009
Page 35
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
