XA-G39 NXP Semiconductors, XA-G39 Datasheet - Page 11

• Manufacturer Part Number: XA-G39
• Description: Xa 16-bit Microcontroller Family Xa 16-bit Microcontroller 32k Flash/1k Ram, Watchdog, 2 Uarts
• Manufacturer: NXP Semiconductors

Philips Semiconductors
FMIDLE
The FMIDLE bit in the AUXR register allows saving additional power
by turning off the Flash memory when the CPU is in the Idle mode.
This must be done just prior to initiating the Idle mode, as shown
below.
When the Flash memory is put into the Idle mode by setting FMIDLE,
restarting the CPU upon exiting Idle mode takes slightly longer,
about 3 microseconds. However, the standby current consumed by
the Flash memory is reduced from about 8mA to about 1mA.
Default Loader
A default loader that accepts programming commands in a
predetermined format is contained permanently in the Boot ROM. A
factory fresh device will enter this loader automatically if it is
powered up without first being programmed by the user. Loader
commands include functions such as erase block; program Flash
memory; read Flash memory; and blank check.
Boot Vector
The XA-G39 contains two special FLASH registers: the BOOT
VECTOR and the STATUS BYTE.
The “Boot Vector” allows forcing the execution of a user supplied
Flash loader upon reset, under two specific sets of conditions. At the
falling edge of reset, the XA-G39 examines the contents of the
Status Byte. If the Status Byte is set to zero, power-up execution
starts at location 0000H, which is the normal start address of the
user’s application code.
When the Status Byte is set to a value other than zero, the Boot
Vector is used as the reset vector (4 bytes), including the Boot
2002 Mar 13
XA 16-bit microcontroller family
32K Flash/1K RAM, watchdog, 2 UARTs
OR
OR
.
AUXR,#$40
PCON,#$01
.
; Set Flash memory
; Turn on Idle mode.
; Execution resumes
to idle mode.
here when Idle
mode terminates.
PROGRAM
ADDRESS
Figure 3. Flash Memory Configuration
7FFF
4000
2000
0000
16 KBYTES
8 KBYTES
8 KBYTES
BLOCK 2
BLOCK 1
BLOCK 0
11
which corresponds to the address F900h for the factory masked-ROM
Program Counter (BPC) and the Boot PSW (BPSW). The factory
default settings are 8000h for the BPSW and F800h for the BPC,
ISP boot loader. The Status Byte is automatically set to a non-zero
value when a programming error occurs. A custom boot loader can
be written with the Boot Vector set to the custom boot loader.
Hardware Activation of the Boot Vector
Program execution at the Boot Vector may also be forced from
outside of the microcontroller by setting the correct state on a few
pins. While Reset is asserted, the PSEN pin must be pulled low, the
ALE pin allowed to float high (need not be pulled up externally), and
the EA pin driven to a logic high (or up to V
released. This is the same effect as having a non-zero status byte.
This allows building an application that will normally execute the end
user’s code but can be manually forced into ISP operation. The Boot
ROM is enabled when use of the Boot Vector is forced as described
above, so the branch may go to the default loader. Conversely, user
code in the program memory space from F800h to FFFFh may not
be executed when the Boot Vector is used.
If the factory default setting for the BPC (F800h) is changed, it will
no longer point to the ISP masked-ROM boot loader code. If this
happens, the only possible way to change the contents of the Boot
Vector is through the parallel programming method, provided that
the end user application does not contain a customized loader that
provides for erasing and reprogramming of the Boot Vector and
Status Byte.
After programming the FLASH, the status byte should be erased to
zero in order to allow execution of the user’s application code
beginning at address 0000H.
NOTE: When erasing the Status Byte or Boot Vector, these
bytes are erased at the same time. It is necessary to reprogram
the Boot Vector after erasing and updating the Status Byte.
SU01591
PP
). Then reset may be
XA-G39
Preliminary data