Sharp DV-MX1U User's Guide download pdf (Page 192)

180 ROM-DOS Commands

MX1 Reference Guide E-EQ-MX1RG-D

Error Conditions

No Extended Memory—An extended memory error condition can occur if the BIOS (via Int

15H, function 88H) notifies HIMEM that there is no extended memory. In this situation, HIMEM

displays an appropriate error message and does not install.

Failure to Control the A20 Line—When HIMEM installs, it attempts to control the A20 line,

which controls access to the HMA. HIMEM first attempts control via the AT method (using the

8259 keyboard control). If that fails, HIMEM then attempts control via the PS/2 method (using

I/O port 60H). If both methods fail, HIMEM assumes it can’t control the A20 line and displays the

message

A20 Control (OFF)

If either of these errors occur, try using the /A20, /A20+, or /PS2 in the HIMEM command line.

Note also that some older programs assume that the machine is a 1MB 8086 and so require that

the A20 line to be disabled (OFF) while they run. Current programs typically do not require that

the A20 line be disabled.

Examples

Device = HIMEM.SYS

Installs the XMS device driver. Once this driver is installed, accessing the HMA and Extended

Memory (XMS) memory areas are legal. The Extended Memory area can contain up to 2GB of

memory. Typical systems have 4

, 8, or 16MB of XMS memory installed.

Device = HIMEM.SYS /machine:1

Forces the use of the AT-style A20 line control.

The HIMEM driver fails to load when either the machine does not have memory above the 1MB

boundary or the BIOS does not provide support for it. It also fails to load when another XMS

manager has been previously installed.

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Sharp DV-MX1U User's Guide Page 192