PC87393F datasheet(35/148 Pages) NSC

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2.0 Device Architecture and Configuration (Continued)

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The Parallel Port pins function as an FDD interface for either drive 1 or drive 3. See Figure 5 for the internal routing between

the PPM and FDC, and the Parallel Port and FDC pin-sets when PPM mode is active. The FDC output signals are driven

simultaneously both on the normal FDC pins and on the corresponding Parallel Port pins. The FDC inputs are received from

the FDC pins when either drive 0 or drive 2 is selected, and from the corresponding Parallel Port pins when either drive 1 or

drive 3 is selected.

The Parallel Port output signals are isolated from the Parallel Port pins. The Parallel Port input signals, as reflected by the

STR register, assume one of two possible values ([BUSY, PE, SLCT, ACK] = 1001 or 1111), indicating that nothing is con-

nected to the Parallel Port. The default values are controlled by bit 2 of the Parallel Port Configuration register (see Section

2.12.3 for details).

PPM is in power save mode when PPM is active and the PPM power save mode bit is enabled.See Section 2.6.1 for details.

2.6.1

PPM Power Save Mode

PPM power save mode helps avoid the additional power consumption associated with driving two sets of FDD outputs by

limiting the activity to the selected drive only. PPM power save mode is enabled by bit 2 of the SIOCF5 register, and is in

effect only when the PPM is active. Assuming that the internal FDD (on the normal FDC pins) is drive 0, while the external

FDD (on the Parallel Port pins) is drive 1, the outputs of the non-selected drive do not toggle, but rather are frozen at their

inactive levels. Table 14 shows the behavior of the FDC outputs on both the FDC and Parallel Port pins when the PPM is

active and PPM power save mode is enabled.

Table 14. FDC Output Status in PPM Power Save Mode

DR0

Signal

DR1

Signal

FDC Outputs

FDC Pins

Parallel Port Pins

Functional

Frozen at inactive levels

Functional

FDC

Parallel

FDC Inputs

Figure 5. PPM Routing

FDC Pins

Parallel Port Pins

Parallel Port Inputs

FDC Outputs

Outputs

PPM Active and

Drive 1 or 3 Selected

PPM in Power Save Mode

and Drive 1 Selected

Parallel Port Input Values

FDC Outputs

FDC Inputs

Default “Non-Connect”

Outputs Frozen

at Inactive Levels

Outputs Frozen

at Inactive Levels

PPM in Power Save Mode

and Drive 0 Selected

PPM Power Save

Port

Parallel Port

PPM Active

and bit 7 of SIOCF5 is ’0’ (PNF=0)

PC87393F Datasheet(PDF) 35 Page - National Semiconductor (TI)

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