Matrix printer only receives ~one character when SEL is pressed

I'm trying to get an OKI microline 3390 to work, and manually sending text to it as demonstrated here: (thirty-minute video) . I understand the printer has to be selected for it to work, which on my model is labelled SEL. An indicator light comes on when I press it. The printer has a mode to print a hex table of the characters coming in. When I send a string of characters to it, it will print only the first. When I then press the SEL button twice, once to deselect, and then to select again, the second character is written. I can repeat this process to have the hex codes of my entire string pri

Question by Minth-11 on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.