Intel 8XC196K Series User Manual page 398

Table of Contents

To program these bits, write the correct value to the location shown in Table 16-5 on page 16-8

using slave programming mode. During normal operation, you can determine the values of these

bits by reading the UPROM special-function register (Figure 16-1).

The unerasable PROM (USFR) register contains two bits that disable external fetches of data and

instructions and another that detects a failed oscillator. These bits can be programmed, but cannot be

WARNING: These bits can be programmed, but can never be erased. Programming these bits makes

dynamic failure analysis impossible. For this reason, devices with programmed UPROM bits cannot

be returned to Intel for failure analysis.

You can verify a UPROM bit to make sure it programmed, but you cannot erase it. For this reason,

Intel cannot test the bits before shipment. However, Intel does test the features that the UPROM

bits enable, so the only undetectable defects are (unlikely) defects within the UPROM cells them-

Reserved; always write as zeros.

Disable External Instruction Fetch

Setting this bit prevents the bus controller from executing external

instruction fetches. Any attempt to load an external address initiates a

Disable External Data Fetch

Setting this bit prevents the bus controller from executing external data

reads and writes. Any attempt to access data through the bus controller

initiates a reset.

Reserved; always write as zero.

Oscillator Fail Detect

Setting this bit enables the device to detect a failed oscillator and reset

itself. (In EPROM packages, this bit can be erased.)

Figure 16-1. Unerasable PROM (USFR) Register

PROGRAMMING THE NONVOLATILE MEMORY

Reset State: