AN2548 Freescale Semiconductor / Motorola, AN2548 Datasheet - Page 4

• Manufacturer Part Number: AN2548
• Description: Serial Monitor Program for HCS12 MCUs
• Manufacturer: Freescale Semiconductor / Motorola

AN2548/D
Vector Redirection and Interrupt Use
4
ensure that a Windows
communications with the monitor, the host must send a carriage return ($0D)
at the correct baud rate. If the monitor detects some other character, the host
baud rate is not correct so it continues to wait in a loop for the $0D character
before printing the first prompt sequence. The host must verify the monitor
baud rate by initially sending a carriage return at 115.2 kbaud. If this is the
correct baud rate, the target MCU will respond with a prompt sequence of $E0,
$08, and a “>” prompt character. The prompt sequence is detailed more
completely in following sections.
Defining AllowSci0 in the S12SerMonxrx.def file enables the monitor to release
the SCI0 port back to the user code in the system as a run/load switch function.
In load mode, the monitor will have full access of the SCI0 port. In RUN mode,
the monitor will check for a valid user SCI0 interrupt vector and jump to this
vector if it is valid.
Access to the user vectors is accomplished via a jump table located within the
monitor memory space. This jump table points all interrupt sources to a
duplicate vector table located just below the monitor ($F780–$F7FE). The
monitor will automatically redirect vector programming operations to these user
vectors. The user code should therefore keep the normal (non-monitor) vector
locations ($FF80–$FFFE). The monitor also checks interrupts as they occur,
and it will re-enter monitor mode if execution of an interrupt with an
unprogrammed vector is attempted. If this occurs, the
Out of Range
implement a software response for all vectors (which is a good programming
practice).
The monitor depends on interrupts being available for monitor re-entry after GO
or TRACE commands. Therefore, the user application must normally have
interrupts enabled. If user code blocks interrupts such as during interrupt
service routines, the serial monitor cannot execute memory access or HALT
commands until interrupts are enabled again.
Freescale Semiconductor, Inc.
For More Information On This Product,
Serial Monitor Program for HCS12 MCUs
Go to: www.freescale.com
error will be returned. The user is strongly encouraged to

-based PC can recognize this as a break. To establish
$E3 — Stack Pointer
MOTOROLA