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Connection of Unused Pins
1.6
Connection of Unused Pins
The correct termination of all unused pins is listed in
.
Table 1-4. Connection of Unused Pins
(1)
Pin
Potential
Comment
AVCC
DV
CC
AVSS
DV
SS
Px.0 to Px.7
Open
Switched to port function, output direction (PxDIR.n = 1)
RST/NMI
DV
CC
or V
CC
47-k
Ω
pullup or internal pullup selected with 10-nF (2.2 nF
(2)
) pulldown
PJ.0/TDO
The JTAG pins are shared with general-purpose I/O function (PJ.x). If not
PJ.1/TDI
Open
being used, these should be switched to port function, output direction.
PJ.2/TMS
When used as JTAG pins, these pins should remain open.
PJ.3/TCK
TEST
Open
This pin always has an internal pulldown enabled.
(1)
Any unused pin with a secondary function that is shared with general-purpose I/O should follow the
Px.0 to Px.7 unused pin connection guidelines.
(2)
The pulldown capacitor should not exceed 2.2 nF when using devices with Spy-Bi-Wire interface in
Spy-Bi-Wire mode or in 4-wire JTAG mode with TI tools like FET interfaces or GANG programmers.
1.7
Reset Pin (RST/NMI) Configuration
The reset pin can be configured as a reset function (default) or as an NMI function via the Special
Function Register (SFR), SFRRPCR. Setting SYSNMI causes the RST/NMI pin to be configured as an
external NMI source. The external NMI is edge sensitive and its edge is selectable by SYSNMIIES.
Setting the NMIIE enables the interrupt of the external NMI. Upon an external NMI event, the NMIIFG is
set.
The RST/NMI pin can have either a pullup or pulldown present or not. SYSRSTUP selects either pullup or
pulldown, and SYSRSTRE causes the pullup or pulldown to be enabled or not. If the RST/NMI pin is
unused, it is required to have either the internal pullup selected and enabled or an external resistor
connected to the RST/NMI pin as shown in
1.8
Configuring JTAG Pins
The JTAG pins are shared with general-purpose I/O pins. There are several ways that the JTAG pins can
be selected for four-wire JTAG mode via software. Normally, upon a BOR, SYSJTAGPIN is cleared. With
SYSJTAGPIN cleared, the JTAG are configured as general-purpose I/O. See the
chapter for
details on controlling the JTAG pins as general-purpose I/O. If SYSJTAG = 1, the JTAG pins are
configured to four-wire JTAG mode and remain in this mode until another BOR condition occurs.
Therefore, SYSJTAGPIN is a write only once function. Clearing it by software is not possible, and the
device does not change from four-wire JTAG mode to general-purpose I/O.
40
System Resets, Interrupts, and Operating Modes, System Control Module
SLAU272C – May 2011 – Revised November 2013
(SYS)
Copyright © 2011–2013, Texas Instruments Incorporated