TMS279X

The TMS279X family are N-channel silicon gate MOS LSl devices which perform the functions of a Floppy Disk Formatter/Controller in a single chip implementation. The TMS279X, which can be considered the end result of both the Western Digital FD1771 and FD179X designs, is IBM compatible in single-density mode (FM) and System 34 compatible in double-density mode (MFM). The TMS279X contains all the features of its predecessor the FD179X plus a high performance phase-lock-loop data separator as well as write precompensation logic. In double-density mode, write precompensation is automatically engaged to a value programmed via an external potentiometer. In order to maintain compatibility, the FD1771, FD179X and TMS279X designs were made as close as possible with the computer interface, instruction set, and I/O registers being identical. Also, head load control is identical. In each case, the actual pin assignments vary by only a few pins from any one to another.

The processor interface consists of an 8-bit bi-directional bus for data, status, and control word transfers.

The TMS279X is set up to operate on a multiplexed bus with other bus-oriented devices.

The TMS279X is TTL compatible on all inputs and outputs. The outputs will drive one TTL load or three LS loads. The 2793 is identical to the 2791 except the DAL lines are true for systems that utilize true data busses.

The 2795/7 has a side-select output for controlling double-sided drives.