CPU OPERATION
POWER CONSUMPTION
The 4C24 is an all CMOS CPU, so overall power consumption is typically less than 3 watts (about
400 mA). If the lowest power consumption is necessary, the CPU clock can be slowed when not
active. This can reduce the CPU power to less than 150 mA. It is the responsibility of the application
program to execute the slow CPU instructions when idle.
4C24's with Cyrix or TI 486SLC 's can be put into a low power mode by simply halting the CPU.
The BIOS keyboard input (Int 16 function 0) routine does this automatically, so application programs
that call this function when waiting for input will use minimum power.
If the absolute lowest power consumption is required, Mesa can supply a version of the 4C24 that
uses a lower power PAL. Please contact MESA for more information on this low power CPU version.
WATCHDOG TIMER
The 4C24 is intended mainly for embedded system applications where there is no one to hit the
reset switch should something go awry. To prevent a crashed or otherwise hung system from
remaining so indefinitely, the 4C24 is provided with a built in watchdog timer that will reset the 4C24
if not 'fed' regularly. The time-out period of this counter is 1.6 seconds. The default INT 1C (user tic
clock) task 'feeds' the watchdog. User software must be careful not to disable interrupts for more
than these time periods or the watchdog may bite!
SERIAL PORTS
The serial ports on the 4C24 are compatible with 16C550A type UARTS . These UARTS have 16
byte receive and transmit FIFO's. The serial ports can be setup by the BIOS to be COM1 and COM2
or COM3 andCOM4 (vide infra). Default setup is COM1 and COM2 (0x3F8 and 0x2F8).
PARALLEL PORT
The 4C24 parallel port is capable of bidirectional operation. The parallel port I/O address can be
set to be at the LPT1, LPT2, or LPT3 locations. Default port location is 0x278.
OTHER I/O
The 4C24 uses the game port chip select in the 82C7XX multi-I/O chip for accessing on card I/O
ports. These ports control the setup EEPROM and the disk emulator hardware. The I/O ports are
located at 200H and 201H. You must make sure that no external I/O cards overlap this area.
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4C24 CPU USER'S MANUAL
