The TWICE cable connects the slave CPU to the prototype system. TWICE stands for TWIN In-Circuit Emulation, indicating that the microprocessor of the prototype is replaced by a special socket and emulated by the TWIN, under control of the TWIN Operating System. The TWICE cable contains active component and is carefully designed to avoid noise and undue signal delays.
The grey ribbon cables connect to the Slave processor in the TWIN system. The colored ribbon cable consists of twisted pairs that connect to a socket that replaces the 2650 microprocessor in the prototype.
The cables are fairly long: 45 cm (10″) from the TWICE box to the CPU socket, and 115 cm (45″) from the TWICE box to the Slave processor. For microprocessors faster than the 2650 the length becomes an issue. Tektronix therefore employed a different approach: they move the slave CPU from the Slave processor card into the TWICE box. The CPU is mounted on a small module that can either plug into the Slave processor card or inside the TWICE box.
There does not appear to be any schematic of the TWICE cable anywhere, not for the 2650 microprocessor not for any other microprocessors. I therefore made the effort of re-creating the schematics. A PDF-version can be downloaded below.
