Q: What types of printers does my Rainbow use?
From Hardware
The Rainbow 100 uses serial printers, not parallel printers. The port is an EIA RS-423 and RS-232-C and CCITT V.28 compliant port. Probably the most popular printer for use with the Rainbow is the DEC LA50, although the more advanced LA75 should also work. Other DEC printers that will work are LQP02 and the LA100. It is theoretically possible to connect a LN03 laser printer also.
The printer port pinouts are as follows:
| Pin | Name | Signal | Description |
| 1 | PROT GND | Protective ground | Chassis Ground |
| 2 | TXD | Transmitted Data (Input) | Data transmitted to the Rainbow computer |
| 3 | RXD | Received Data (Output) | Data transmitted from the Rainbow computer |
| 5 | CTS | Clear to Send | Always on |
| 6 | DSR | Data Set Ready | Upon power-up, Rainbow turns this signal on |
| 7 | SGND | Signal Ground | Common ground for all signals |
| 20 | DTR | Data Terminal Ready | Indicates printer status. If printer turns this off, Rainbow stops sending chars to printer. When printer turns on DTR, Rainbow sends chars to printer. |
Any pins not listed are not used by the Rainbow 100.