TC7660 Powers RS232 Data Loop (TC7660, TC7660H, TC7660S)
For reliable operation the optoisolator should be biased to saturation, so: IOPTO = + = 2k The introduction of single-voltage EPROMS and dynamic RAMs has permitted designers to produce complete digital systems powered by a single 5V supply. One area which has not yielded to single-supply operation, however, is the RS-232 interface. If a system must communicate with an RS-232 serial device, such as a printer or another computer, a separate power supply is required.
TC7660, RS-232, Data Loop, Low Cost Adapter, AN8