Texas Instruments ADS1254, Руководство пользователя, Страница: 20 / 40

Reset Switch
3-4
3.2 Reset Switch
Switch SW1 is a miniature pushbutton which, when pressed, forces the MCUs
RESET line low. When released, the MCU enters a reset cycle. If
communication becomes disrupted between the host and the board, or the
board is unresponsive, pressing RESET returns the system to normal
operation.
3.3 Connectors
The various connectors on the ADS1254EVM are described in this section.
3.3.1 J7: RS-232 Connector
The host PC controls the board through this connector, which is a 9-pin female
D-shell type, pinned out in the usual manner. Certain of the flow control lines
are used for special purposes by the ADS1254EVM board; these are
described in the table.
In the RS-232 electrical specification, − 5 V to –15 V on a line indicates a logic
high (mark), and 5 V to 15 V indicates logic low (space). Line states are
described here according to their logical states.
If a non-handshaking RS-232 cable is used, that is, one which connects only
RD, TD, and signal ground. The board can still operate normally, but it cannot
be reset by the host PC, and bootstrap firmware upgrading cannot be
performed through the serial port (it can still be done through the JTAG port
J6, but this requires a special programming adapter and software).
Table 3−2. J7: RS-232 Port Pinout
Pin
Number Signal
Name RS-232 Name Direction
(at board) Function
1 DCD Data carrier detect Output None
2 RD Receive data Output Serial data output to host PC
3 TD Transmit data Input Serial data input from host PC
4 DTR Data terminal ready Input Connected to the MCUs reset circuit. A low
on this line resets the MCU. Must be held
high for normal operation
5 SG Signal ground Power Ground reference
6 DSR Data set ready Output None
7 RTS Request to send Input Connected to TCK on MCU. Used for boot-
strap firmware loading. Must be held high
for normal operation
8 CTS Clear to send Output None
9 RI Ring indicator Output None