I want to use CD4051 as the RX expansion of USART serial port, but how to calculate the baud rate that CD4051 can meet...

chuzhaonan

I want to use CD4051 as the RX expansion of USART serial port, but how to calculate the baud rate that CD4051 can meet... [Copy link]

 

I want to use CD4051 as the RX expansion of USART serial port, but how to calculate what baud rate communication the CD4051 speed can meet?

dcexpert

The speed of the gate circuit is much higher than the serial port rate, so don't worry too much. For specific parameters, please refer to the relevant data sheet.

chuzhaonan

dcexpert posted on 2019-9-8 22:11 The speed of the gate circuit is much higher than the speed of the serial port, so don't worry too much. For specific parameters, please refer to the relevant data sheet

Which parameter in the specification is the speed of the gate circuit?

dcexpert

chuzhaonan posted on 2019-9-8 22:13 Which parameter in the specification is the speed of the gate circuit?

It mainly depends on the signal rise/fall delay, which is usually in the ns level. Of course, there are differences between different models. Please refer to the manual for details.

maychang

If the power supply voltage is 5V, it is recommended to use 74HC4051. 74HC4051 is much faster than CD4051 and allows a larger output current, but the maximum power supply voltage is relatively small.

qwqwqw2088

This IC is used for serial port expansion. The speed of serial port communication is called baud rate, which is the number of bits transmitted per second. The selected baud rate can be used to reversely calculate the working frequency of the IC.

The theoretical delay time is related to the input signal voltage

chuzhaonan

qwqwqw2088 posted on 2019-9-9 08:24 This IC is used for serial port expansion. The speed of serial port communication is called baud rate, which is the number of bits transmitted per second. The selected baud rate can be used to reverse the working frequency of the IC...

Can you be more specific?

For example, for a 3.3V system with a baud rate of 38400, how do we infer the relationship between the IC's operating frequency and theoretical delay time?

chuzhaonan

dcexpert posted on 2019-9-8 22:15 chuzhaonan posted on 2019-9-8 22:13 What parameter in the specification is the speed of the gate circuit? It mainly depends on the delay of the signal rise/fall, ...

Can you be more specific?

For example, for a 3.3V system with a baud rate of 38400, how do we infer the relationship between the IC's operating frequency and theoretical delay time?

dcexpert

chuzhaonan posted on 2019-9-9 15:27 Can you explain it in detail? For example, for a 3.3V system with a baud rate of 38400, how do you infer the relationship between the IC's operating frequency and the theoretical delay time?

The serial port is a low-speed communication, and the gate circuit is a high-speed circuit. The orders of magnitude of the two differ by several levels. Basically, there is no need to consider the delay problem, only the level matching needs to be considered.

Taking TI's CD4051 as an example, the input-to-output delay can be regarded as a fixed offset, which has little effect on serial communication and is very small.

The maximum delay comes from channel switching. After selecting the address, there will be a relatively large delay in opening and closing the channel.

For serial communication, if the baud rate is 38400, the transmission time of each bit is 1/38400 = 26us. This is much longer than the previous delay. Unless the baud rate reaches 1M or above, there is no need to consider it.

bigbat

@ maychang is right, 74HC4051 is faster than CD4051. CD4051 is an analog channel, which is not good for serial port. In fact, the speed of serial port is relatively high compared to the speed of analog. The analog channel focuses on the analog resistance rather than the switching speed, so in some cases it does not have the "Schmitt" characteristic, which is easy to cause false operation.

chuzhaonan

dcexpert published on 2019-9-9 21:22 The serial port is a low-speed communication, and the gate circuit is a high-speed circuit. The order of magnitude difference between the two is several levels. Basically, there is no need to consider the delay problem, only the level matching...

If my power supply is 5V, then I have to consider that the serial port baud rate should be less than 1/(Propagation Delay Time(Address-to-Signal OUT (Channels ON or OFF))+Propagation Delay Time(Inhibit-to-Signal OUT (Channel Turning ON))+Propagation Delay Time(Inhibit-to-Signal OUT (Channel Turning OFF))) right?

chuzhaonan

dcexpert published on 2019-9-9 21:22 The serial port is a low-speed communication, and the gate circuit is a high-speed circuit. The order of magnitude difference between the two is several levels. Basically, there is no need to consider the delay problem, only the level matching...

I don't quite understand this diagram. TrTf is the time of the rising edge and the falling edge, right? What does 10%50%90% mean?