Serial port expansion

Find a broken circuit board under the table today see a chip GM8125, the main function of this chip is to expand the serial port.

GM8125 can be a full-duplex standard serial port expansion into 5 standard serial port, and through the external pin to control the serial port expansion mode: Single channel operation mode and multi-channel operation mode, that can specify a sub-serial port and the mother serial port with the same baud rate of a single work, Also allows all the sub-serial port in the mother serial baud rate based on the simultaneous operation.
When the chip works in multi-channel mode, the sub-serial port can actively respond to the data sent from the machine, and sent to the host by the mother serial port, and return the sub-serial address. This mode enables each slave to send the request can be timely response, even if all the slave at the same time send the request, the data will not be lost, the basic realization of the main control unit and peripheral communication real-time performance.
The operating baud rate of the chip mother serial port and the sub-serial port can be adjusted by software without modifying the external circuit and crystal frequency. The chip has less external control, flexible application, simple programming and is suitable for most systems with serial port expansion requirements.

2 characteristics
--write control word to control the chip--each sub-serial port baud rate adjustable (unified adjustment)--data format 10-bit or 11-bit optional
--single channel mode, maximum baud rate support 20Mbps, multi-channel mode, sub-serial port maximum baud rate 38400bps--sub-serial number: 5
--A PIN-select chip works in single-channel mode or multi-channel operation mode
--in the single channel operation mode, the chip work without initialization settings, working serial port by the Address line control selection-in the multi-channel operation mode, the baud rate of each sub-port is equal to the female serial port baud rate 6 Division-in the multi-channel operation mode, the receiving address line sradd2~0 to the MCU to return the address of the receiving channel MCU
After receiving the data sent by the mother serial port, we can judge the data from which sub-serial port from the Sradd2~0 state, and send the data from the MCU to the mother serial port, and then to the standard serial communication format, TTL level output-wide working voltage: 2.3~6.7v
--output baud rate error less than 0.2%, input baud rate error requirement is less than 2.8%-sampling 16 times per bit, improve data correctness
--The input address pin has a 50~80kωpull-down resistor and the other input pins have 50~80kωpull-up power
Resistance (except Osci)

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Serial port expansion