This is a correction of old memoes on modem timing synchronization written in 1985 at Codex Corp., a subsidiary of Motorola. In the memos, many aspects and implementation details are discussed in detail. The products developed based on these memos in mid-80s were probably the earliest commercial Modems with digital timing technology available in the world. Since then this technology are widely used today, it should still have reference value to engineers and researchers working in this area.