HCS500

DS40153B-page 14

Preliminary

© 1997 Microchip Technology Inc.

5.0

DECODER PROGRAMMING

The decoder uses a 2K, 24LC02B serial EEPROM. The memory is divided between system memory that stores the

transmitter information (read protected) and user memory (read/write). Commands to access the user memory are

described in Sections 4.2.5 and 4.2.6.

The following information stored in system memory needs to be programmed before the decoder can be used:

•

64-bit manufacturer’s code

• Decoder configuration byte

5.1

Configuration Byte

The decoder is configured during initialization by setting the appropriate bits in the configuration byte. The following table

list the options:

5.1.1

LRN_MODE

LRN_MODE selects between two learning modes. With LRN_MODE = 0, the normal (serial number derived) mode is

selected; with LRN_MODE=1, the secure (seed derived) mode is selected. See Section 6.0 for more detail on learning

modes.

5.1.2

LRN_ALG

algorithm is selected; with LRN_ALG = 1, the XOR algorithm is selected. See Section 6.0 for more detail on learning

algorithms.

5.1.3

REPEAT

The HCS500 can be configured to indicate repeated transmissions. In a stand-alone configuration, repeated transmis-

sions must be disabled.

Note 1: These memory locations are read protected and can only be written to using the program command with

the device powered up.

2: The contents of the system memory is encrypted by a unique 64-bit key that is stored in the HCS500. To

initialize the system memory, the HCS500’s program command must be used. The EEPROM and HCS500

are matched, and the devices must be kept together. In-circuit programming is therefore recommended.

Bit

Mnemonic

Description

0

LRN_MODE

Learning mode selection

LRN_MODE = 0—Normal Learn

LRN_MODE = 1—Secure Learn

1

LRN_ALG

Algorithm selection

LRN_ALG = 1—XOR Algorithm

2

REPEAT

Repeat Transmission enable

0 = Disable

1 = Enabled

3

Not Used

Reserved

4

Not Used

Reserved

5

Not Used

Reserved

6

Not Used

Reserved

7

Not Used

Reserved