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PC8477BVF-1 Datasheet(PDF) 23 Page - National Semiconductor (TI) |
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PC8477BVF-1 Datasheet(HTML) 23 Page - National Semiconductor (TI) |
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23 / 54 page  40 Command Set Description (Continued) If IDENT is low the DENSEL pin is active low for the 500 kbs or 1 Mbs data rates In addition to these modes the DENSEL output can be set to always low or always high as shown in Table 4-2 This will allow the user more flexibili- ty with new drive types Note The DENSEL output values shown below are with the INVERT pin tied low If the INVERT pin is tied high the outputs shown below have the opposite polarity TABLE 4-2 DENSEL Decoding Bit 1 Bit 0 DENSEL Pin Definition 0 0 low 0 1 high 1 0 undefined 1 1 DEFAULT TABLE 4-3 DENSEL Default Encoding Data Rate DENSEL (default) IDENT e 1 IDENT e 0 250 kbs low high 300 kbs low high 500 kbs high low 1 Mbs high low BFR CMOS Disk Interface Buffer Enable 0 e Drive output signals configured as standard 4 mA push-pull outputs (actually 48 mA sink 4 mA source) (default) 1 e Drive output signals configured as 48 mA open- drain outputs WLD Scan Wild Card 0 e An FF (hex) from either the mP or the disk during a Scan command is interpreted as a wildcard charac- ter that will always match true (default) 1 e The Scan commands do not recognize FF (hex) as a wildcard character Head Settle Time allowed for readwrite head to settle af- ter a seek during an Implied Seek operation Data Rate HST Range 250 kbs N x 8 0 – 120 ms 300 kbs N x 667 0 – 100 ms 500 kbs N x 4 0 – 60 ms 1 Mbs N x 2 0 – 30 ms Note N e 8 (default) HST e Head Settle Time RG Read Gate Diagnostic 0 e Enable DSKCHG disk interface input for normal op- eration (default) 1 e Enable DSKCHG to act as an external Read Gate input signal to the Data Separator This is intended as a test mode to aid in evaluation of the Data Sep- arator PU PUMP Pulse Output Diagnostic 0 e Enable MFM output pin for normal operation (de- fault) 1 e Enable the MFM output to act as the active low out- put of the Data Separator charge pump This signal consists of a series of pulses indicating when the phase comparator is making a phase correction This Pump output will be active low for a pump up or pump down signal from the phase comparator and is intended as a test mode to aid in the evaluation of the Data Separator 427 NSC Command The NSC command can be used to distinguish between the PC8477B version and the Intel 82077AA The result Phase byte uniquely identifies the floppy controller as a PC8477B which returns a value of 73 hex The 82077AA and DP8473 return a value 80h signifying an invalid command The lower four bits of this result byte are subject to change by NSC and will reflect the particular version of the PC8477B part Note The PC8477A will return a value of 72h in the result phase of the NSC command 428 Perpendicular Mode Command The Perpendicular Mode command is designed to support the unique Format and Write Data requirements of Perpen- dicular (Vertical) Recording disk drives (4 Mbytes unformat- ted capacity) The Perpendicular Mode command will con- figure each of the four logical drives as a perpendicular or conventional disk drive Configuration of the four logical disk drives is done via the D3 – D0 bits or with the GAP and WG control bits This command should be issued during the ini- tialization of the floppy controller Perpendicular Recording drives operate in ‘‘Extra High Den- sity’’ mode at 1 Mbs and are downward compatible with 144 Mbyte and 720 kbyte drives at 500 kbs (High Density) and 250 kbs (Double Density) respectively If perpendicular drives are present in the system this command should be issued during initialization of the floppy controller which will configure each drive as perpendicular or conventional Then when a drive is accessed for a Format or Write Data command the floppy controller will adjust the Format or Write Data parameters based on the data rate (see Table 4-4) Looking at the second command byte DC3 – DC0 corre- spond to the four logical drives A ‘‘0’’ written to DCn sets drive n to conventional mode and a ‘‘1’’ sets drive n to perpendicular mode Also the OW (Overwrite) bit offers ad- ditional control When OW e 1 changing the values of DC3 – DC0 (drive configuration bits) is enabled When OW e 0 the internal values of DC3 – DC0 are unaffected regardless of what is written to DC3 – DC0 The function of the DCn bits must also be qualified by set- ting both WG and GAP to 0 If WG and GAP are used (ie not set to 00) they will override whatever is programmed in the DCn bits Table 4-4A indicates the operation of the PC8477B based on the values of GAP and WG Note that when GAP and WG are both 0 the DCn bits are used to configure each logical drive as conventional or perpendicu- lar DC3 – DC0 are unaffected by a software reset but WG and GAP are both cleared to 0 after a software reset A hardware reset will reset all the bits to zero (conventional mode for all drives) The Perpendicular Mode command bits may be rewritten at any time Note When in the Perpendicular Mode for any drive at any data rate via the DC3–DC0 bits write precompensation is set to zero 23 |
Similar Part No. - PC8477BVF-1 |
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Similar Description - PC8477BVF-1 |
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