Previous multifunction cards required that a secondary function be "mapped" to a different slot in the computer's memory, rendering that slot unusable. This card was unique in the sense that it did not use "Phantom Slots" to achieve this functionality.
By combining the functions of two cards into one, the Serial Pro freed up an extra slot for those with highly populated machines.
The Serial Pro was a multifunction serial interface and clock/calendar card from Applied Engineering. Laser 128: under the ROM behind the metal cover on the bottom.Apple IIe: under the CD ROM (or CF ROM in later models).The No-Slot Clock was usually installed in the following locations on the motherboard in the following computers: Once the driver was installed it emulated the Thunderclock. The No-Slot Clock was both ProDOS and Dos 3.3 compatible, however a software driver had to be patched into ProDOS or integrated into the applicable DOS 3.3 program. A user had to remove the ROM from its socket, insert the No-Slot Clock, and then reinsert the ROM chip into the top of the No-Slot Clock. In an Apple II, the No-Slot Clock resided under any 28-pin ROM chip, including one on a peripheral card. The non-replaceable battery had a life expectancy of 10 years. The clock was powered by an embedded lithium battery, electrically disconnected until power was first applied to retain freshness. Dallas Semiconductor produced the device as an easy implementation for a real-time clock for a variety of applications. The No-Slot Clock, also known as the Dallas Smartwatch (DS1216E), was a 28-pin chip-like device that could be used directly in any Apple II or Apple II compatible with a 28-pin ROM. 3 Thunderclock Plus (Thunderware Incorporated).