MaximIntegrated 16-2
MAX31782 User’s Guide
Revision 0; 8/11
SECTION 16: TEST ACCESS PORT (TAP)
The MAX31782 incorporates a test access port (TAP) and TAP controller for communication with a host device across
a 4-wire synchronous serial interface . The TAP can be used by the MAX31782 to support in-system programming and/
or in-circuit debug . The TAP is compatible with the JTAG IEEE standard 1149 and is formed by four interface signals
as described in
. For detailed information on the TAP and TAP controller, refer to IEEE STD 1149 .1 “IEEE
Standard Test Access Port and Boundary-Scan Architecture .”
Table16-1.TestAccessPortPins
These pins default to the TAP/JTAG function on reset, which means that the part is always ready for in-circuit debugging
or in-circuit programming operations following any reset . Once an application has been loaded and starts running, the
TAP/JTAG port can still be used for in-circuit debugging operations . If in-circuit debugging functionality is not needed,
the associated port pins can be reclaimed for application use by setting the TAP bit (SC .7) bit to 0 . This disables the
TAP/JTAG interface and allows the four pins to operate as normal port pins . See
.
Figure 16-1. TAP and TAP Controller
EXTERNALPINSIGNAL
FUNCTION
TDO
(Test Data Output)
Serial-Data Output . This signal is used to serially transfer internal data to the external host . Data
is transferred least significant bit first . Data is driven out only on the falling edge of TCK, only dur-
ing TAP Shift-IR or Shift-DR states and is otherwise inactive .
TDI
(Test Data Input)
Serial-Data Input . This signal is used to receive data serially transferred by the host . Data is
received least significant bit first and is sampled on the rising edge of TCK . TDI is weakly pulled
high internally when TAP = 1 .
TCK
(Test Clock Input)
Serial Shift Clock Provided by Host . When this signal is stopped at 0, storage elements in the
TAP logic must retain their data indefinitely . TCK is weakly pulled high internally when TAP = 1 .
TMS
(Test Mode Select Input)
Mode Select Input . This signal is sampled at the rising edge of TCK and controls movement
between TAP states . TMS is weakly pulled high internally when TAP = 1 .
TDO
TDI
WRITE
TCK
DEBUG
UPDATE-DR
UPDATE-DR
V
DD
TAP CONTROLLER
TMS
SYSTEM PROGRAM
READ
POWER-ON
RESET
BYPASS
INSTRUCTION REGISTER
7
6
5
4
3
2
1
0 s1 s0
2
1
0
2
1
0
V
DD
