C541U Datasheet, PDF (43/63 Pages) Siemens Semiconductor Group – 8 BIT CMOS MICROCONTROLLER

C541U
Table 9
Access Modes Selection
Access Mode
Program OTP memory byte
Read OTP memory byte
Program OTP lock bits
Read OTP lock bits
Read OTP version byte
EA/
V_PP ^PROG
V_PP
V_IH
H
V_PP
V_IH
H
V_IH
H
PRD
H
PMSEL
1
0
HH
HH L
L
H
Address
(Port 2)
Data
(Port 0)
A0-7
A8-15
D0-7
–
D1,D0 see
table 10
Byte addr.
of sign. byte
D0-7
Lock Bits Programming / Read
The C541U has two programmable lock bits which, when programmed according tabie 10, provide
four levels of protection for the on-chip OTP code memory. The state of the lock bits can also be
read.
Table 10
Lock Bit Protection Types
Lock Bits at D1,D0 Protection Protection Type
D1
D0
Level
1
1
Level 0 The OTP lock feature is disabled. During normal operation of
the C541U, the state of the EA pin is not latched on reset.
1
0
Level 1 During normal operation of the C541U, MOVC instructions
executed from external program memory are disabled from
fetching code bytes from internal memory. EA is sampled and
latched on reset. An OTP memory read operation is only
possible using the OTP verification mode for protection level 1.
Further programming of the OTP memory is disabled
(reprogramming security).
0
1
Level 2 Same as level 1, but also OTP memory read operation using
OTP verification mode is disabled.
0
0
Level 3 Same as level 2; but additionally external code execution by
setting EA=low during normal operation of the C541U is no
more possible.
External code execution, which is initiated by an internal
program (e.g. by an internal jump instruction above the ROM
boundary), is still possible.
Semiconductor Group
41