machine — direct hardware access

import machine

Read / write 8-, 16-, 32-bit values at arbitrary linear addresses in protected mode. On DOS under PMODE/W this gives you access to the entire 32-bit address space — conventional + extended memory, ISA bus, VGA frame buffer, etc.

⚠️ There is no protection. Writing to the wrong address can hang DOS, crash PMODE/W, or scribble on PMODE/W’s own internal structures. This is the lowest-level interface in MicroPython — use it the way you’d use a debugger’s “edit memory” feature.

machine.mem8 / machine.mem16 / machine.mem32

Subscriptable read/write at the given address:

import machine

# VGA text-mode buffer is at linear 0xB8000 (each cell is 2 bytes:
# attribute + char).
machine.mem16[0xB8000] = 0x0F41        # bright white 'A' at top-left

# Read it back
print(hex(machine.mem16[0xB8000]))     # '0xf41'

# Read 4 bytes at the BIOS data area's tick counter:
ticks = machine.mem32[0x46C]
print('BIOS ticks since midnight:', ticks)

The base address is a flat 32-bit linear address. PMODE/W identity-maps conventional memory (below 1 MB), so 0xB8000 is the actual VGA buffer.

Use cases

Read BIOS data area

# Equipment word at 0x410
equip = machine.mem16[0x410]
print('serial ports:', (equip >> 9) & 7)
print('floppies:', (equip >> 6) & 3)

Write a marker to VRAM

# Top-left of color text mode: blink + green-on-blue '@'
machine.mem16[0xB8000] = 0x1A40

Snoop / replace an interrupt vector

# Real-mode IVT entry for INT 0x21
ivt_21 = (machine.mem16[0x21 * 4 + 2] << 16) | machine.mem16[0x21 * 4]
print(f'INT 21 handler at 0x{ivt_21:08x}')

(For a PM IDT entry, see how dosint21.py does it — different table.)

Constants

There aren’t any built-in constants for memory regions; you supply the linear address.

Not implemented

The wider machine module that microcontroller MicroPython exposes — machine.Pin, machine.I2C, machine.SPI, machine.UART, machine.RTC, machine.WDT, machine.Timer — is NOT provided. DOS has no pin model; ISA peripherals would each need a typed driver.

The lower-level machine.mem* accessors are enough to talk to ISA devices directly. For a real RTC you can call INT 1Ah AH=2 via dosint21.

See also

Credit: surface from MicroPython machine docs (MIT). DOS context is this port’s.