TMS279X (WD279X) FLOPPY DISK FORMATTER / CONTROLLER FAMILY

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When both HLD and HLT are true, the 279X will then read from or write to the media. The AND of HLD and

HLT appears as status bit 5 in Type I status.

In summary, for Type I commands: if h = 0 and V = 0, HLD is reset. If h = 1 and V = 0, HLD is set at the

beginning of the command and HLT is not sampled nor is there an internal 15 ms delay. If h = 0 and V = 1,

HLD is set near the end of the command, an internal 15 ms occurs, and the 279X waits for HLT to be true. If

h = 1 and V = 1, HLD is set at the beginning of the command. Near the end of the command, after all the

steps have been issued, an internal 15 ms delay occurs and the 279X then waits for HLT to occur.

For Type II and III commands with E flag off, HLD is made active and HLT is sampled until true. With E flag

on, HLD is made active, an internal 15 ms delay occurs and then HLT is sampled until true.

restore (seek track 0)

Upon receipt of this command, the track 00 (TR00) input is sampled. If TR00 is active low, indicating the

read-write head is positioned over track 0, the track register is loaded with zeroes and an interrupt is

generated. If TR00 is not active low, stepping pulses at a rate specified by the r1 r0 field are issued until the

TR00 input is activated. At this time the track register is loaded with zeroes and an interrupt is generated. If

the TR00 input does not go active low after 255 stepping pulses, the 279X terminates operation, interrupts,

and sets the seek error status bit. A verification operation takes place if the V flag is set. The h bit allows the

head to be loaded at the start of command. Note that the Restore command is executed when M R goes

from an active to an inactive state.

seek

This command assumes that the track register contains the track number of the current position of the

read-write head and the data register contains the desired track number. The TMS279X will update the track

register and issue stepping pulses in the appropriate direction until the contents of the track register are

equal to the contents of the data register (the desired track location). A verification operation takes place if

the V flag is on. The h bit allows the head to be loaded at the start of the command. An interrupt is generated

at the completion of the command. Note: when using multiple drives, the track register must be updated for

the drive selected before seeks are issued.