HD63265 Floppy Disk Controller Users Manual 2ed Mar89 - Bitsavers

6.7 Command Code Rejection6.7.1 PhenomenonThe FDC rejects command codes under the following timing conditions: (1)within the period 2.25 us before to 1.75 ~s after the IRQ signal is assertedto request a CIS command caused by READY signal inversion in 8-inch mode(or 4.5 ~s before to 3.5 ~s after IRQ assertion in 5-inch mode); or (2) ifthe IRQ signal has been asserted to request a CIS command when READY signalinversion is detected. This malfunction is described below for each timingcondition.Command Rejection Timing Condition 1: From 2.25 ~sbefore to 1.75 ~safter the IRQ signal is asserted to request a CIS command initiated by theREADY signal in 8-inch mode (or 4.5 ~s before to 3.5 ~s after IRQ assertionin 5-inch mode)In 8-inch mode, the FDC rejects all commands except ABORT if those commandsare issued within the period 2.25 ~s before to 1.75 ~s after (or 4.5 ~s beforeto 3.5 ~s after in 5-inch mode) the IRQ signal is asserted to request a CIScommand initiated by READY signal i~version, as shown in figure 6-60. Thetime during which commands are rejected is indicated by period A. In addition,for 0.5 ~s (1.0 ~s in 5-inch mode) (period B) after period A, the FDCaccepts commands but the BSY bit of the status register (STR) remainscleared. The BSY bit of the STR is set when the host system writes thefirst-byte parameter to the FDC. Changes in the STR according to the timingof each issued command are summarized in table 6-15. Note that the FDC willnot reject a command if the IRQ signal is asserted to request a CIS commandinitiated by SEEK or RECALIBRATE command completion.HITACHI 75