Applied Data Systems Bitsy Plus, User Manual, Page: 35 / 68

Feature Reference
ADS document # 110114-1001A Page 25
Using Stereo Headphones and Speakers in the Same System
Some applications use both headphones and
speakers. You can wire the headphone jack to
automatically switch the amplifier to single-ended
mode when a headphone plug is inserted in the jack.
This will disable the drive to any speakers that are
wired into the system.
Most headphone jacks include mechanical switches
that indicate when a headphone plug has been
inserted. The diagram at right shows a circuit that pulls down the HP_IN signal when a
headphone plug is removed.
For this circuit to work reliably in differential mode, the HP_IN signal must remain below V
HP_IN
through the largest output voltage swings of SPKR_L. Use of 1 k
Ω
resistors meets this
requirement.
4.5 Data Communications
The Bitsy Plus has several built-in channels for communication with peripheral and peer devices.
These include RS-232 and logic-level serial, USB host and client ports, SPI bus and I
2
C.
4.5.1 Serial Ports
The Bitsy Plus has three StrongARM serial ports configured as follows:
Port # signals Connector Standard Factory options
Serial 1 9-wire J10 RS-232 (9-wire) 3.3 V CMOS
Serial 2 3-wire J3 3.3 V CMOS (none)
Serial 3 5-wire J3 RS-232 3.3 V CMOS
The StrongARM serial ports supply two signals: TX and RX ("three-wire" serial, counting GND).
The Bitsy Plus uses StrongARM GPIO lines to generate additional signals (RTS and CTS for
Serial 3 plus DTR, DSR, DCD and RI for Serial 1). See section 4.1.6 for details.
The StrongARM can configure Serial 2 as an IrDA port . It should be used in conjunction with
the IrDAOn signal (J3), which enables the IrDA transmitter. IrDA transceivers can be panel
mounted or placed on a personality board.
4.5.2 USB
The Bitsy Plus includes signals for USB 1.1 Host and Client ports. The USB Host (downstream)
functionality is driven by the SA-1111 companion chip, while the USB Client ("Function" or
upstream) port is managed by the SA-1110 processor. The Bitsy Plus can be configured as a self-
powered hub, with one Host and one Client port
To create a USB connection, you must wire a standard USB socket as described in the following
sections. For each type of connector, pin numbering is as follows:
Pin USB signal
1 USB_PWR
2 USB -
3 USB +
4 GND