Zenith Z-100 Series, Reference Manual

Page: 53 / 163

Page 4.8
Central Processing Unit
Programming CPU Functions
The portion of this manual on programming the CPU operations will, of necessity,
be brief. The operations are largely "housekeeping" types of routines. Also included
are functions which cannot be otherwise put into the other sections.
Induded here are system functions which will print screen routines, determine
I/O configuration, determine memory size, and set and read the time-of-day. A
method for programming rudimentary sound, at the assembly language level, is
also provided. Use of these functions assumes you have a knowledge of this level
of programming.
System Functions
Interrupts 5H, IIH, 12H, and IAH are used to call a desired system function
through the 8088 microprocessor.
Interrupt 5H — Print Screen Contents
When this interrupt is implemented, the contents of the screen are dumped to
an attached printer. Only valid characters will be printed. Graphics containing
characters not recognized by the printing device will be ignored.
As an aid when using the print screen routine, a byte of global RAM has been
reserved at address 0050:0000 as a status byte. During execution of the print
screen function this byte is set to a value of I, which represents a flag value
used by the routine to prevent other print screen requests from interrupting an
already executing dump. Upon completion of the operation, the status byte will
be changed to 0 if there were no errors, or to FFH if an error was encountered.
The most common error would be a printer time-out error.
Interrupt 11H — Determine I/O Configuration
This function is useful when applications programs need to know what hardware
is installed in the system. The hardware configuration is
returned as bi t-m apped
data in 8088 register AX as defined in Table 4.3.
0