ETS2228 Maintenance Manual
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Page 13, Total 43
Figure 10 keypad implements circuit
Figure 1 keypad back facet circuit
Asynchronous serial port drive circuit
We put the drive of the serial port onto the serial port line. The output power level
of
the serial port drive does not match the MSM6000 power level---The high power level of MSM6000 is
2.8V, while the high power level of the serial port drive is 4.4V. Thus, what is needed is to make a
power-level conversion and protection circuit for the transistor to convert the power level of the serial
port circuit. The dual transient suppression diode protects the serial port and prevents the damage
towards the system from abnormal power level input such as ESD.
Serial port signals are divided into 5 groups:
1) Data receiving signal RS_RD (Input); Data sending signal RS_TD (Output).
2) Traffic signal clearing/sending RS_CTS(Input); Request sending RS_RTS (Output)
3) Modem status signal (modem refers to FWT); Carrier wave detection UART1_DCD (Output);
Data terminal ready UART1_DRT (Output)
4) Serial port indicating UART1_IND (Output). The power level (high/low) is determined by the
serial port line. The power level differentiates debugging data line and high-speed data line. Low power
level indicates high-speed (230400BPS) and high power level indicates low speed
(115200BPS).
5) External serial port drive power supply VDD1_RS. The power switch is controlled by the
MSM_P voltage.
The circuits are shown by the following diagrams:
