The Tascam Digital Interface[1] (TDIF) is a proprietary format connector defined by TASCAM that is unbalanced and uses a 25-pin D-sub cable to transmit and/or receive up to eight channels of digital audio between compatible devices.
(cite: DA-88 users manual) Later TASCAM products included the ability to sync to the TDIF-1 connection, although that still excluded the DA-88.
This is because the TDIF-1 spec was derived from the digital audio transmitter of the NEC uPD6381 DSP used in the DA-88.
The TDIF-1 Version 1.1 specification includes parity and other channel information bits.
[3] The TASCAM X-48 supports 96 kHz at full channel count over 6 TDIF-1 connectors, using a post Version 2.0 specification.