
LXT9785 and LXT9785E Advanced 8-Port 10/100 Mbps PHY Transceivers
158
Datasheet
Document Number: 249241
Revision Number: 010
Revision Date: 30-May-2006
The LXT9785/LXT9785E includes an IEEE 1149.1 boundary scan test port for board level testing.
All digital input, output, and input/output pins are accessible.
4.12.4
Boundary Scan Interface
This interface consists of five pins (TMS, TDI, TDO, TCK and TRST_L). It includes a state
machine, data register array, and instruction register. The TMS and TDI pins are internally pulled
up and the TCK pin is internally pulled down. TDO does not have an internal pull-up or pull-down.
4.12.5
State Machine
The TAP controller is a 16-state machine driven by the TCK and TMS pins. Upon reset, the
TEST_LOGIC_RESET state is entered. The state machine is also reset when TMS and TDI are
High for five TCK periods.
4.12.6
Instruction Register
The IDCODE instruction is always invoked after the state machine resets. The decode logic
ensures the correct data flow to the Data registers according to the current instruction. Valid
4.12.7
Boundary Scan Register
Each Boundary Scan Register (BSR) cell has two stages. A flip-flop and a latch are used for the
serial shift stage and the parallel output stage. There are four modes of operation as listed in
Table 48. Refer to the Identification Information section in the LXT9785/LXT9785E Specification
Update (document number 249357) for the JTAG ID numbers.
Table 48. BSR Mode of Operation
Mode
Description
1Capture
2Shift
3
Update
4
System Function
Table 49. Supported JTAG Instructions
Name
Code
Description
Data
Register
EXTEST
0000 Hex
External Test
BSR
IDCODE
FFFE Hex
ID Code Inspection
ID REG
SAMPLE
FFF8 Hex
Sample Boundary
BSR
High Z
FFCF Hex
Force Float
Bypass
Clamp
FFEF Hex
Clamp
BSR
BYPASS
FFFF Hex
Bypass Scan
Bypass