Zilog EZ80F916 - Manual (Page 162)

UM014423-0607 Using the ANSI C-Compiler
ZiLOG Developer Studio II
eZ80Acclaim! ® User Manual
142
}
}
}
}
In summary, setting up interrupts is somewhat complex on the eZ80
®
family as there are a
number of things to configure, such as the I register, the long and short jump tables, and so
on. Because the eZ80F92 and eZ80F93 only have two byte addresses for the default inter-
rupt vectors, you need to set up other jump tables to bridge the gap into the 24-bit world
when using those CPUs. The other thing to keep in mind is that the I register controls the
upper 8 bits of this default interrupt vector, allowing you to move the overall interrupt
jump table anywhere in the 64K range.
Placement Directives
The eZ80 Acclaim! C-Compiler provides language extensions to declare a variable at an
address and to align a variable at a specified alignment. The following sections describe
placement directives:
•
“Placement of a Variable” on page 142
•
“Placement of Consecutive Variables” on page 143
•
“Alignment of a Variable” on page 143
Placement of a Variable
The following syntax can be used to declare a global or static variable at an address:
char placed_char _At 0xB7E100; // placed_char is assigned an address 0xB7E100
struct {
char ch;
int ii;
} ss _At 0xB7E110; // ss is assigned an address 0xB7E110
const char init_char _At 0x1000 = 33;
// init_char is in rom at 0x1000 and initialized to 33
NOTE: Only placed variables with the
const
qualifier can be initialized. Non-
const
placed variables are not re-initialized correctly upon program reset.The
uninitialized placed variables are not initialized to zero by the compiler startup
routine.