Secure mode indicator for smart phone or PDA

A digital system, comprising:

• a central processing unit (CPU) for executing instructions;
• a graphics display for displaying results of the executed instructions;
• a public memory connected to an instruction bus of the CPU for holding nonsecure instructions, the nonsecure instructions including an activation sequence of instructions starting at an entry point address, the public memory being always accessible by the CPU;
• a secure memory connected to the instruction bus of the CPU for holding secure instructions, the secure memory being accessible only when a security signal is asserted;
• security circuitry having an output for asserting the security signal when a secure mode of operation is established, comprising a security state machine (SSM) connected to the CPU for monitoring a set of status signals and connected to the instruction address bus for monitoring instruction address signals, the SSM having an output for asserting the security signal when a secure mode of operation is established;
• and
• a secure mode indicator, independent from the graphics display and responsive to the security signal, the secure mode indicator being observable by a user of the digital system,
• wherein the secure mode indicator can only be placed in an active mode by executing an instruction while the security signal is asserted;
• and wherein the SSM has the entry point address hard coded and is operable to monitor execution of an activation sequence of instructions located in the public memory and to enter the secure mode of operation only if the activation sequence of instruction is executed by the CPU in a pre-defined order hard coded in the SSM.