DIGITAL Extension Parameters
AH
=
DOH ReturnsAL
=
The contents of days-since-read counterex =
High-order 16 bits of elapsed-time DX = Low-order 16 bits of elapsed-timeThis function returns the contents of the days-since-read counter and the elapsed-time. The days-since-read counter indicates the number of 24-hour pe-riods that have passed since any of Interrupt 1AH functions OOH. 01H, or DOH was executed. The elapsed-time is a 32-bit value measured in timer ticks.
This function is similar to function OOH, except that AL returns days-since-read instead of the 24-hour overflow flag. The 24-hour overflow flag indicates only that 24 hours or more have elapsed.
Executing this function clears the 24-hour overflow flag and the days-since-read counter.
15 - 140 Chapter 15 -ROM BIOS Interrupt lAH
Interrupt IBH: Keyboard Break
Software Interrupt - Industry-Standard Parameters
None Returns Nothing
Whenever the key combination CtrllBreak is typed. at the keyboard, the routine pointed to by this vector is executed by interrupt 09H. Use an IRET instruc-tion to return control to interrupt 09H. The ROM BIOS initializes this vector to point to a ROM BIOS IRET.
Interrupt lCH: Timer Tick
Software Interrupt - Industry-Standard Parameters
None Returns Nothing
When a system clock interrupt occurs, the ROM BIOS executes Interrupt lCH. Thus, the routine pointed to by this vector is executed. Use an IRET instruction to return control to the ROM BIOS. The ROM BIOS initializes this vector to point to a ROM BIOS IRET. For additional information, see
Interrupt OSH.
Chapter 15 - ROM BIOS Interrupt IBH and lCH 15 - 141
Interrupt IDH: Video Parameters
Pointer - Industry-Standard
This vector points to a table, not executable code.
This vector is not a true interrupt. This table is 16 bytes long and corresponds directly with the registers RO through R15 of the 6845 video controller. For additional information on the video controller, see Chapter 7.
15 - 142 Chapter 15 - ROM BIOS Interrupt IBH and lCH
Interrupt lEH: Diskette Parameter Tables
Pointer - Industry-Standard
This vector points to a table, not executable code.
A diskette parameter table defines the physical characteristics of a diskette.
The values in the table are used by the diskette driver to initialize the diskette controller. Table 15-16 describes the contents of a diskette parameter table.
Each parameter in Table 15-16 is one byte long.
The interrupt vector for interrupt 1EH points to the diskette parameter table.
If a diskette drive does not exist, the interrupt vector for interrupt 1EH is reserved and undefined.
Table 15-16 Diskette Parameter Table Description Offset
OOH
01H
02H
Bits 7-4
Description Step rate
Each increase in the value of bits 7-4 decreases the step rate by 1 ms, so that zero equals 16 ms, one equals 15 ms, two equals 14 ms, and so on.
3-0 Head unload time
7-1
Each increase in the value of bits 3-0 increases the head unload time by 16 ms, so that zero equals 16 ms, one equals 32 ms, two equals 48 ms, and so on.
Head load time
Each increase in the value of bits 7-1 increases the head load time by 2 ms, so that zero equals 2 ms, one equals 4 ms, two equals 6 ms, and so on.
o
Direct Memory Access {DMAI selection7-0
o
= Do not use DMA 1 = Use DMA modeClock ticks until motor is turned off
Chapter 15 - ROM BIOS Interrupt 1EH 15 - 143
Table 15-16 Diskette Parameter Table Description ~cont.}
Offset Bits Description
03H 7-0 Sector size
Each increase in value doubles the sector size, so that zero equals 128 bytes, one equals 256 bytes, two equals 512 bytes, and so on. The default is value is two (512 bytes}.
04H 7-0 Sectors per track ~8, 9. 10, or 15) 05H 7-0 Sector gap length (1BH}
06H 7-0 Data length (FFH) 07H 7-0 Format gap length (54H) 08H 7-0 Format fill byte (F6H)
09H 7-0 Head settle time in milliseconds
OAH 7-0 Motor start-up time in .125 second increments
15 - 144 Chapter 15 - ROM BIOS Interrupt lEH
Interrupt IFH: Graphics Character Table Pointer
Pointer - Industry-Standard with DIGITAL Extension
This vector points to a table, not executable code. It points to a character table for generation of character codes BOH through FFH. Interrupt 10H, function DOH extends the functionality of this pointer. If enabled, this vector points character table for generation of character codes OOH through FFH.
Interrupt 40H: Revector of Interrupt 13H
Software Interrupt - Industry-Standard
Normally, the diskette 110 is serviced through interrupt 13H. When a hard disk is installed, the hard disk 110 is serviced through interrupt 13H, and the
diskette I/O service is revectored to Interrupt 40H. This revectoring informa-tion is provided only for clarity. Always use Interrupt 13H for both diskette and hard disk functions.
Chapter 15 - ROM BIOS Interrupt IFH and 40H 15 - 145
Interrupt 4tH and 46H: Hard Disk Parameter Tables
Pointer - Industry-Standard
This vector points to a table, not executable code.
A hard disk parameter table defines the physical characteristics of a hard disk.
The values in the table are used by the hard disk driver to initialize the hard disk controller. Table 15-17 describes the contents of a hard disk parameter table.
The hard disk parameter tables are located in DIGITAL private RAM. During the power-up sequence, the disk type is extracted from CMOS RAM. If the disk type is unknown, the table contains all zeros. If the disk type is one of the 14 industry-standard types, the table is initialized from the hard disk data in the ROM BIOS. If the disk type is the DIGITAL extended type OFH, the ROM BIOS expects the boot block to contain the parameters. The ROM BIOS initializes the table with data extracted from the boot block. (As part of its initialization process, the FDISK utility writes the parameters in the boot block. I
The interrupt vectors for Interrupt 41H and 46H point to the hard disk para-meter tables for hard disk 0 and hard disk 1, respectively. If hard disk 1 does not exist, the interrupt vector for Interrupt 46H is reserved and undefined.
15 - 146 Chapter 15 . ROM BIOS Interrupt 41H and 46H
Table 15-17 Hard Disk Parameter Table Description Offset
OOH 02H 03H 05H 07H OBH
09H OCH OEH OFH
Size 1 Word 1 Byte 1 Word 1 Word 1 Byte 1 Byte
3 Bytes 1 Word 1 Byte 1 Byte
Description
Maximum number of cylinders on hard disk drive Maximum number of heads on hard disk drive Not used
Cylinder number to start using write precompensation
Not used
Control byte sent to controller
If bit 7 or bit 6 is set (1 I, disable retries
If bit 3 is set (11, hard disk has more than eight heads
Not used Landing zone
Number of sectors per track Reserved for future use
Chapter 15 - ROM BIOS Interrupt 41H and 46H 15 - 147
Interrupt 4AH: RTC Alarm
Software - Industry-Standard
When a real-time clock alarm occurs. the ROM BIOS executes Interrupt 4AH.
Thus, the routine pointed to by this vector is executed. Use an IRET instruc-tion to return control to the ROM BIOS. For addiinstruc-tional informainstruc-tion, see Interrupt 1AH (functions 06H and 07HI.
Interrupt 70H: Real-Time Clock
Hardware Interrupt - Industry-Standard
Interrupt 70H provides the ROM BIOS with hardware-interrupt services for the real-time clock. This interrupt monitors the periodic interrupt and the alarm interrupt.
Using this interrupt requires knowledge of the VAXmate hardware, the ROM BIOS, and the operating system. For informtion about the real-time clock, see Chapter 5. For information about the ROM BIOS clock services, see Interrupt 1AH.
Interrupt 71H: Redirect to Interrupt OAH
Hardware Interrupt - Industry-Standard
This interrupt redirects the IRQ9 hardware interrupt to Interrupt OAH, which is the old IRQ2 hardware interrupt. IRQ9 is an available interrupt input and Interrupt OAH is an available interrupt vector.
15 - 148 Chapter 15 - ROM BIOS Interrupt 4AH, 70H, and 71H
Interrupt 72H: Local Area Network Controller (LANCE)
Hardware Interrupt - DIGITAL Extension
Interrupt 72H provides the network software with hardware-interrupt services for the LANCE. This interrupt service provides an operation complete indica-tion from the LANCE.
Interrupt 72H has no arguments. preserves all registers, and returns no values.
Using this interrupt requires knowledge of the VAXmate hardware, the ROM BIOS, and the operating system. For more information on the LANCE, see Chapter 13. For more information about network I/O services, see the
VAXmate Network Technical Reference Manual.
Chapter 15 - ROM BIOS Interrupt 728 and 738 15 - 149