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Compaq Deskpro 4000N and 4000S Personal Computers 5-9 First Edition - September 1997 Chapter 5 Input/Output Interfaces Chapter 5 Input/Output InterfacesDISKETTE DRIVE INTERFACE The diskette drive interface supports up to two diskette drives through a standard 34-pin diskette drive connector. All Deskpro 4000S models include a 3.5 inch 1.44-MB diskette drive installed as drive A. There is no physical provision for a second drive (B). The diskette drive interface function is integrated into the 87307 I/O controller component. The internal logic of the I/O controller is software-compatible with standard 82077-type logic. The diskette drive controller has three operational phases in the following order: . Command phase - The controller receives the command from the system. . Execution phase - The controller carries out the command. . Results phase - Status and results data is read back from the controller to the system. The Command phase consists of several bytes written in series from the CPU to the data register (3F5h/375h). The first byte identifies the command and the remaining bytes define the parameters of the command. The Main Status register (3F4h/374h) provides data flow control for the diskette drive controller and must be polled between each byte transfer during the Command phase. The Execution phase starts as soon as the last byte of the Command phase is received. An Execution phase may involve the transfer of data to and from the diskette drive, a mechnical control function of the drive, or an operation that remains internal to the diskette drive controller. Data transfers (writes or reads) with the diskette drive controller are by DMA, using the DRQ2 and DACK2- signals for control. The Results phase consists of the CPU reading a series of status bytes (from the data register (3F5h/375h)) that indicate the results of the command. Note that some commands do not have a Result phase, in which case the Execution phase can be followed by a Command phase. During periods of inactivity, the diskette drive controller is in a non-operation mode known as the Idle phase. 5-10 Compaq Deskpro 4000N and 4000S Personal Computers First Edition – September 1997 Technical Reference Guide Technical Reference GuideDISKETTE DRIVE PROGRAMMING 5.3.1.1 Diskette Drive Interface Configuration The diskette drive controller must be configured for a specific address and also must be enabled before it can be used. Address selection and enabling of the diskette drive interface are affected by firmware through the PnP configuration registers of the 87307 I/O controller. The PnP configuration registers are accessed through I/O registers 15Ch (index) and 15Dh (data). The diskette drive I/F is initiated by firmware selecting logical device 3 of the 87307. This is accomplished by the following sequence: 1. Write 07h to I/O register 15Ch. 2. Write 03h to I/O register 15Dh (this selects the diskette drive I/F). 3. Write 30h to I/O register 15Ch. 4. Write 01h to I/O register 15Dh (this activates the interface). The diskette drive I/F configuration registers are listed in the following table: Table 5-6. Diskette Drive Interface Configuration Registers Index Reset Address Function R/W Value 30h Activate R/W 01h 31h I/O Range Check R/W 00h 60h Base Address MSB R/W 03h 61h Base Address LSB R/W F0h 70h Interrupt Select R/W 06h 71h Interrupt Type R/W 03h 74h DMA Channel Select R/W 02h 75h Report DMA Assignment RO 04h F0h Configuration Data R/W - F1h Drive ID R/W - Compaq Deskpro 4000N and 4000S Personal Computers 5-11 First Edition - September 1997 Chapter 5 Input/Output Interfaces Chapter 5 Input/Output InterfacesDiskette Drive Interface Control The BIOS function INT 13 provides basic control of the diskette drive interface. The diskette drive interface can be controlled by software through I/O-mapped registers listed in Table 5-7. Table 5-7. Diskette Drive Interface Control Registers Primary Alternate Address Address Register R/W 3F1h 371h Media ID R 3F2h 372h Drive Control W 3F4h 374h Main Status R 3F5h 375h Data R/W 3F7h 377h Drive Status R Data Transfer Rate W The base address (3F1h or 371h) and enabling of the diskette drive controller is selected through the Function Enable Register (FER, addr. 399.00h) of the 87307 I/O controller. Address selection and enabling is automatically done by the BIOS during POST but can also be accomplished with the Setup utility and other software. The following paragraphs describe the diskette drive interface control registers. Media ID Register, I/O Port 3F1h/371h (Read Only) Bit Function 7..5 Media Type: xx1 = Invalid 000 = 5.25 inch drive 010 = 2.88 MB (3.5 inch drive) 100 = 1.44 MB (3.5 inch drive) 110 = 720 KB (3.5 inch drive) 4..2 Reserved 1,0 Tape Select: 00 = None 10 = Drive 2 01 = Drive 1 11 = Drive 3 Drive Control Register, I/O Port 3F2h/372h (Write Only) Bit Function 7,6 Reserved 5 Drive 2 Motor 0 = Off, 1 = On 4 Drive 1 Motor 0 = Off, 1 = On 3 Interrupt / DMA Enable 0 = Disabled, 1 = Enabled 2 ...
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