Initial User Cpu Register Values; Sysclk Field; Iobase Field - Motorola M68EVB912B32 User Manual

D-BUG12 CUSTOMIZATION DATA

INITIAL USER CPU REGISTER VALUES

The first seven fields in the CustomData typedef struct are used to provide default
values for the user CPU12 registers. In this version of D-Bug12, the user CCR value is set to
0x90. This sets the S-bit, disabling the STOP instruction, and the I-bit, inhibiting IRQ interrupts.
The X-bit is cleared to allow the use of the XIRQ interrupt as a user-supplied programmer's
switch when operating in EVB mode. The user SP value is set to 0x0a00 when operating in EVB
mode, which is one byte beyond the last on-chip RAM location available to the user. The
CPU12 stack pointer points to the last byte pushed onto the stack.
When operating the M68EVB912B32 in POD mode, the values in the table for the CCR and the
Stack Pointer are not used. Instead, when the target processor is reset by using the RESET
command, the target's CCR is set to 0xd0. The stack pointer is set to one byte beyond the end of
the target system's RAM, as specified by the DEVICE command.
In both operating modes, all of the other registers are initialized with the values contained in the
customization data table.

SysClk FIELD

The SysClk field is used to inform D-Bug12 of the system clock frequency, M. Its value, in
Hz, is set to 8,000,000. In this implementation, the E-clock frequency is the same as the system
clock frequency, M. SysClk is used by the D-Bug12 BAUD command in calculating the new
value of the SCI Baud register for the requested baud rate.
It is the responsibility of the startup code to perform any actions
necessary to set the system clock frequency. D-Bug12 does not set
or change the system clock frequency using the SysClk value.

IOBase FIELD

The IOBase field defines the base address of the I/O registers. This address is used by
D-Bug12 when accessing the I/O registers associated with the SCI and when programming or
erasing the on-chip EEPROM. On the MC68HC912B32, the I/O registers are mappable to any
2-Kbyte memory space. Therefore, the IOBase entry should only be a multiple of 2048. The
value of IOBase is set to 0x0000, which is the default address of the I/O registers for the
MC68HC912B32.
D-2
NOTE
68EVB912B32UM/D