MD-1 Modem Byte-Back Co Platform(s): ZX80 ZX81 TS 1000 Model: MD-1 Price: $99.95 Includes RS-232 port. Related Content Experimenting With The Byte Back Modem (document) ZCOMM 2K and 16K manual (document) Advertisements SYNC v2 n1 p. 14 Tags RS232, Byte-Back Co, TS 1000, ZX80, ZX81 People No people associated with this content.