UART Frame = Sart bit + number of data bits + Stop bits

Where number of data bits may 5, 6,7,8, and 9 bits

I noticed that UART communication allows for data bits between 5 and 9 bits, with 8 bits being the most common configuration. This can be done on 8-bit, 16-bit, and 32-bit microcontrollers. Have you ever attempted to configure it for 5 bits? If not, I'm curious about the practicality of sending only 5 bits on an 8-bit microcontroller. It seems that if you have a one-character variable and mask 3 bits to send only 5 bits, the receiver will still receive 1 byte

 

Five data bits were used for a Teletype's bauddot code. 5 bits provides for capital letters, numbers, and a few special characters.

 

The receiver will receive a number between zero and 31.

 

Five data bits were used for a Teletype's bauddot code. 5 bits provides for capital letters, numbers, and a few special characters.

How did they do that when there are 26 letters and 10 digits?

In answer to the original question: the hardware simply sends the low 5 bits of the 8-bit byte placed to the transmit register. Or maybe it is the high 5.

 

How did they do that when there are 26 letters and 10 digits?

There’s a code that switches it between numeric and alphabetic. A 1888 version of the “escape sequence”!

 

There’s a code that switches it between numeric and alphabetic. A 1888 version of the “escape sequence”!

The Baudot 'shift' character would cause a mechanical move to the alternate character set on the old machines.

 

Sorry, I forgot the detail about switching to alternate character sets when I typed my reply in the middle of the night, but I did provide a link that explains it.

The lack of civility here is beyond belief.

 

Sorry, I forgot the detail about switching to alternate character sets when I typed my reply in the middle of the night, but I did provide a link that explains it.

The lack of civility here is beyond belief.

Please, people are having fun with old technology here, there's no lack of civility.

 

The lack of civility here is beyond belief.

I hope you are not referring to me. I simply asked how it was done.

 

How did they do that when there are 26 letters and 10 digits?

In answer to the original question: the hardware simply sends the low 5 bits of the 8-bit byte placed to the transmit register. Or maybe it is the high 5.

There were two shift characters called FIGS (Figure Shift) and LTRS (Letter Shift). Letter Shift is the default state, so sending a FIGS changes the shift mode from Letters to Figures (Numbers). A subsequent LTRS would change the shift mode back again. RO-28 Teletype machines, using the Baudot Code, were use on the Stock Exchange and the National Weather service well into the 1970's. Amateur Radio operators still use Baudot Code for RTTY (Radio Teletype) communications.

 

There were two shift characters called FIGS (Figure Shift) and LTRS (Letter Shift). Letter Shift is the default state, so sending a FIGS changes the shift mode from Letters to Figures (Numbers). A subsequent LTRS would change the shift mode back again. RO-28 Teletype machines, using the Baudot Code, were use on the Stock Exchange and the National Weather service well into the 1970's. Amateur Radio operators still use Baudot Code for RTTY (Radio Teletype) communications.

One of my old recurring nightmares is about the teletype school I attended at Radioman A school. First had typing class on old Baudot Code machines using random code groups that you had to copy almost perfectly for 5 min. I wasted so many party hours learning to type on the monsters. Then we (Teletype (TTY) Repairman) trained in the electrical and mechanical operation of the devices to repair them, a much easier class for me than typing. They were still using TTY machines well into the 80's.
https://nara.getarchive.net/media/r...-machine-in-the-maintenance-department-67891b

This guys typing class experience mirrors mine almost exactly.
NSFW language

 

One of my old recurring nightmares is about of the teletype school I attended at Radioman A school. First had typing class on old Baudot Code machines using random code groups that you had to copy almost perfectly for 5 min. I wasted so many party hours learning to type on the monsters. Then we (Teletype (TTY) Repairman) trained in the electrical and mechanical operation of the devices to repair them, a much easier class for me than typing. They were still using TTY machines well into the 80's.
https://nara.getarchive.net/media/r...-machine-in-the-maintenance-department-67891b
View attachment 304134
This guys typing class experience mirrors mine almost exactly.
NSFW language

I had a feeling this was part of your experience. Great stuff!

 

Now I see it doesn't matter that the size of the variable, whether it's one byte / four bytes, or we're using an 8-bit microcontroller / a 32-bit microcontroller, When Uart configured for 5 bits. In this configuration, the sender will only transmit either the higher 5 bits or the lower five bits, and the receiver will receive only those five bits.

 

UART Frame = Sart bit + number of data bits + Stop bits

Where number of data bits may 5, 6,7,8, and 9 bits

I noticed that UART communication allows for data bits between 5 and 9 bits, with 8 bits being the most common configuration. This can be done on 8-bit, 16-bit, and 32-bit microcontrollers. Have you ever attempted to configure it for 5 bits? If not, I'm curious about the practicality of sending only 5 bits on an 8-bit microcontroller. It seems that if you have a one-character variable and mask 3 bits to send only 5 bits, the receiver will still receive 1 byte

If only five bits are sent, then there are only five bits for the receiver to receive. But those five bits are going to be stored in whatever size location it is put, so if that is a 16-bit register (or whatever) five of those bits will be the receive bits and the rest will be something else. Where the five bits end up within that 16 bits and what the "something else" is that the rest of the bits end up being depends on the hardware and/or the software that is running things.

 

It is a fact that all UARTS transmit the LSB (Least Significant Bit) first "on the wire". Similarly, all UARTS receive the LSB (Least Significant Bit) first "from the wire". Regardless of the data length setting, the bits always occupy the Least Significant Bist of the data register in the hardware for both transmit and receive.