For those unaware, DEC is the abbreviation for Digital Equipment Corp. They were a prominent manufacturer of computers and computer related products under the trademark "Digital." They led the computer industry from 1960 to 1990.
Back in the 1980s I built a Heathkit H89 computer. The printer port was RS232 serial. Most of the printers of that time had the Centronics parallel interface. I came into possession of a couple of used DEC LA-180 printers. The printer had a parallel interface that was almost Centronics compatible. In order to use this printer with my Heathkit H89 computer I had to design and build a serial to parallel converter.
Here's a picture of the LA-180 printer in use with my computers in 1985. The printer used continuous fan-fold computer paper. It was a large floor model with a metal base.
This is the circuit I designed to perform the serial to parallel conversion. It's fairly simple. It was based on one I previously designed to work with a Centronics interface. This one was slightly modified to work with the different DEC LA-180 protocol. As I recall, that Demand signal was the key as it controlled whether the printer was ready to accept a new character. The Demand signal from the printer influences the CTS (Clear To Send) signal on the serial side. The MC14411 IC is a crystal controlled baud rate generator. One of the dip switches would be closed to select the baud rate the computer would be using on its serial port. Serial data comes in and gets sent to the AY-3-1015-D UART. This IC does the actual serial to parallel conversion. The data from the UART gets passed through two 7417 ICs. The LA-180 printer parallel input is TTL but requires more current than the UART could provide directly. The 7417s deliver sufficient current to properly drive the printer input. The UART strobes the printer when a character is ready. The printer controls the serial converter with the Demand line to signal that it can take more data.
The Serial Interface option that DEC provided for the LA-180 Printer is DEC part number 54-13166-00. I am not really sure why DEC thought they needed so much circuitry to do the conversion than what I used. I did mine with four ICs and a crystal. Theirs might have provided more than just serial RS232 especially considering they used 50-pin ribbon cable jacks. It looks like the large IC might be a UART. This part is being sold used today for $175 so you could imagine what it cost when it was new.