Dave Smith's company found interest in a cooperative effort with Roland. In 1983, the invention of the musical instrumental digital interface as a standard for digital code transmission digital technology development spurred on more great development in keyboard technology. As now keyboards from totally different manufacturers could communicate through an inexpensive cable. The Sequential Circuits Prophet 600 and the Roland Jupiter 6 communicated at the NAMM trade show and Yamaha soon had the standard implemented into their DX synthesizers which would outsell all previous keyboards.
The Yamaha DX7, the most well known synth of the 1980s, used entirely digital circuitry leaving it free from the need of calibration, and vast numbers of parameters that could be accessed. The "FM" synthesis method was something that had not been explored to near this depth. Most synthesizers before this were subtractive. i.e. You start with a very harmonic-laden sound and you selectively subtract from them using low, high or bandpass filters, or some other methods that tended to result in stranger sounds like ring modulation. Also in 1983 Dave Smith's company SCI marketed the first polyphonic synthesizer keyboard that could play more than one sound at a time called the 'Six-Trak'. It had a six track sequencer and each track could access a different sound. The same year the SCI Prophet T8 with optical key sensing became the first piano action emulating midi keyboard.
But the remaining companies after ARP's demise that had produced analog synthesizers rapidly began to feel the stress. Roland and Korg also of Japan maintained with some innovations of their own and each had 'hit' keyboards I've heard that total DX series unit sales were on the order of 1 Million. The others from Roland and Korg over 250,000. The success of the D50 and M1 was riding on the back of the Kurzweil K250 which first really applied this technology well in 1984. This machine was the first full digital workstation with facilities to sample acoustic sounds with a microphone and play them back with a rate that is proportioned for the note being struck. Many great samples were included in the unit including a piano sound that is still used in the 2000s. And the samples can be routed through a synthesizer architecture of some kind.
Initially some companies steered away from emulating the subtractive synthesis in the digital realm because it was difficult to model how a filter would respond to these complex signals. By the early '90s some fairly good implementations were beginning to appear. The Peavey DPM series also touted as the first keyboards that could import samples which were not 'sampling keyboards'. They also were the first to use off the shelf DSP chips, which emulated the response of analog filters. This sample playback technology also spawned a vast number of inexpensive consumer units called home keyboards which were sold in electronics stores. As the price of memory began to plummet every company was making keyboards of this type. Casio and Yamaha have led sales in these types of units which feature built in speaker systems, usually can run from batteries or power adapters, and have a library of samples with very limited editing if any. They often use cheap plastic strips of keys to keep cost down.
On a different note, the Kurzweil K150 and the Kawai K5 explored additive synthesis where harmonics can be proportioned to make different tones while enveloping groups of them differently in the mid '80s. RMI had explored this to a limited extent in 1974 with the harmonic synthesizer they produced. It should also be mentioned that they were producing the earliest electric piano machines in 1970. This less common synthesis method is also used in Kawai's last synthesizer product series, the K5000's from 1996. Organs like the Hammond B3 use drawbars to control harmonic content of the tone. But the K5000 has an envelope for each harmonic in the entire audio spectrum and dynamic filter control over that for vast possibilities in sound creation.