Uart; Usb - Siemens SXG 75 Service Repair Documentation

17 UART

The UART at the accessory connector requires the status signals CTS, RTS, and DCD to be
configured as a "DCE" device. This has DCD and CTS as outputs, and RTS as an input. However,
TX and RX are configured as a "DTE" device, with TX output and RX input.
UART1 on the MSM6250 is configured as a full "DTE" device, with TX and RX as above, but with
DCD and CTS as inputs, and RTS (RFR) as an output. CTS and RTS (RFR) are connected directly
to the UART hardware block, so their functionality cannot be changed.
DCD is connected to a GPIO pin.
To make the two compatible, connections are required as follows:
• MSM_UART1_TXD. Data output from MSM6250. Connects to TX/D+ pin.
• MSM_UART1_RXD. Data input to MSM6250. Connects to RX/D- pin.
• MSM_UART1_CTS_N. Control input to MSM6250. Connects to RTS pin.
• MSM_UART1_RFR_N. Control output from MSM6250. Connects to DATA/CTS pin.
• MSM_UART1_DCD_N. Control output from MSM6250. Connects to CLK/DCD pin.
Swapping the RTS and CTS signals as above allows these signals to be directly connected to
accessories without modifying the function of UART1. The signal "switch" is made at the EMI filter
Z1200.DCD becomes an output (DCE) function rather than an input. This requires a modification to
the software driver. The TX and RX pins on the accessory connector are switched between USB
and UART functions as required.
UART operation is selected by holding USB_RS232_SEL1 (GPIO83) low. The UART needs to be
selected in order to detect the function of a newly connected accessory.

18 USB

USB data is supported using two pins on the accessory connector. These pins are switched
between USB and UART functions as required. USB operation is selected by holding
USB_RS232_SEL1 (GPIO83) high. SXG75 supports USB data transfer at 12Mbits/sec.
A separate USB power input is not provided. If a USB accessory supports charging, the supply is
present at the same POWER pin as used by battery chargers. Therefore there is only one charging
pass transistor (V1100). No USB power output is provided.
The MSM6250 contains a dedicated USB controller core. This interfaces to a USB transceiver core
on the PM6650. The PM6650 provides the USB interface D+ and D- lines. The PM6650 USB
transceiver is powered from an internal 3.3V supply. This supply is generated from the 5V boost
switching supply on the PM6650. Interfaces between the controller and transceiver are shown
below:
USB controller and transceiver
Technical Documentation
TD_Repair_L3_SXG75_R1.0.pdf
Company Confidential
2006©BenQ
Release 1.0
01/2006
Page 69 of 73