HD63265 Floppy Disk Controller Users Manual 2ed Mar89 - Bitsavers

6.5.8 SEEKBit D7 D6 D5 D4- D3 D2 Dl DoCommand Code 0 0 0 0 1 1 1 1Command x x x x x x US 1 usaparameter.. NCNResult parameter ---Figure 6-45.SEEK CommandIn the SEEK operation (figure 6-45), a drive's head is moved onto the trackspecified by the command parameter's NCN (New Cylinder Number) byte. Thestepping rate (step pulse interval) is specified by the SPECIFY command.Ready Checking: Timing for the ready check conforms to section 5, "Polling".If the ready signal of the drive selected is inactive at the start or duringthe command execution, the step pulse output is halted immediately, and theSED (seek end) and DNR (drive not ready) bits of SSBO are set. The command isterminated abnormally and a request for issuing the CHECK INTERRUPT STATUScommand is made by setting the IRQ signal active.Drive Seek Bits Setting: After the ready signal has been checked, the driveseek bit (DOS-D3S) of the status regi"Ster (STR) corresponding to the drive forwhich the command was issued is set. The drive seek bits can be reset only byissuing the CHECK INTERRUPT STATUS or ABORT command after the seek operation.Direction Signal (HDIR) Setting: Command parameter's NCN and FDC's PCN(physical cylinder number) bytes are compared:If NCN > PCN, HDIR is setIf NCN < PCN, HDIR is resetHDIR is undefined (lor 0) when NCN=PCNPCN Setting: Step pulse count is calculated from the PCN and NCN values afterwhich the NCN value is substituted for PCN. Accordingly, the head's actualphysical address will differ from the PCN value if a command ends (abnormal enddue to change in state of ready signal, or end by ABORT command) before allstep pulses are issued. The head's physical address will also differ from thePCN value if a second SEEK command is issued to a drive while it is seeking.When issuing the SEEK command, make sure that the drive seek bit of the statusregister corresponding to the drive to which the command is issued is zero.HITACHI 57