VRS51L1050
ISP Program Start Conditions
VRS51L1050 IAP feature
Setting the ISP page configuration to a value other
than 0 will cause the processor to jump to the base
address of the ISP boot code when a hardware reset is
performed (provided that the value FFh is present at
program address 0000h).
The VRS51L1050 IAP feature refers to the processor’s
ability to self-program the Flash memory from within
the user program. Five SFR registers control the IAP
operation. The description of these registers is
provided in the following sections.
When the ISP page configuration is set to 0 at the
moment the device is programmed using a parallel
programmer, the ISP boot feature will be disabled.
System Control Register
By default, upon reset the IAP feature of the
VRS51L1050 is deactivated. The IAPE bit of the
SYSCON register is used to enable (and disable) the
VRS51L1050 IAP function.
An alternate way to force the VRS51C1050 to jump to
the ISP boot program is to maintain pins P2.6 and
P2.7 or pin P4.3 at a low logic level during a hardware
reset, as shown in the diagram below:
TABLE 6: SYSTEM CONTROL REGISTER (SYSCON) – SFR BFH
7
6
5
4
3
2
1
0
FIGURE 5: VRS51C1050 ALTERNATE ISP BOOT PROGRAM ACCESS
XRAME
PDWAKEUP
IAPE
ALEI
10ms
10ms
Bit
Mnemonic Description
7
6
5
4
Unused
Unused
Unused
PDWAKEUP
-
-
-
P2.7
Power down wakeup from INT0 / INT1
0 = Deactivated
1 = Device can wakeup from power down
from external interrupt
-
IAP function enable bit
0 = IAP function is deactivated
1 = IAP function is activated
768 byte on-chip enable bit
0 = Enabled
P2.6
RES
3
2
Unused
IAPE
1
0
XRAME
ALEI
OR...
1 = Disabled
ALE output inhibit bit, used to reduce EMI.
0 = ALE pin is active
10ms
10ms
1 = ALE is inhibited
P4.3
RES
IAP Flash Address and Data Registers
The IAPFADHI and IAPADLO registers are used to
specify the address at which the IAP function will be
performed.
TABLE 7:IAP FLASH ADDRESS HIGH - SFR F4H
7
6
5
4
3
2
2
1
1
0
0
The ISP boot program can also be accessed via the
LJMP instruction. When the ISP page configuration is
set to 0 while the device is being programmed with a
parallel programmer, the ISP boot feature will be
disabled.
IAPFADHI[15:8]
TABLE 8:IAP FLASH ADDRESS LOW - SFR F5H
7
6
5
4
3
IAPFADLO[15:8]
The IAPFDATA SFR register contains the data byte
required to perform the IAP function.
TABLE 9:IAP FLASH DATA REGISTER - SFR F6H
7
6
5
4
3
2
1
0
IAPFDATA[7:0]
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