# 5 Configuration Dictionary The configuration dictionary is a key-value store containing all the options necessary for the proper functioning of ExpressLink modules. All keys are case sensitive. Configuration key-value pairs listed in Table 2 are meant to be long lived (persist) throughout the life of the application and so are stored in non-volatile memory. Note that these key-value pairs have factory preset values, and can be read only or write only. **Table 2 - Configuration dictionary persistent keys** | Configuration Parameter | Type | Initial Value | Factory Reset | Buff Size | Description | | --- | --- | --- | --- | --- | --- | | About | R | Vendor - Model | N | 64 | A concatenation of Vendor name and Model name. | | Version | R | X.Y.Z | N | 32 | The specific module firmware version. | | TechSpec | R | TechSpec version | N | 16 | The Technical Specification version this model implements (for example 'v0.6', 'v1.1'). | | ThingName | R | UID | N | 64 | The UID provided by the HW root of trust and present in the device certificate (also see [9.1.3 ExpressLink Birth Certificate](elpg-provisioning.md#elpg-provisioning-birth-certificate)). | | Certificate | R | Device Birth Certificate | N | ≥4KB | Device certificate used to authenticate with AWS cloud, signed by the manufacturer CA (also see [9.1.3 ExpressLink Birth Certificate](elpg-provisioning.md#elpg-provisioning-birth-certificate)). | | CustomName | R/W | \$1empty\$1 | Y | ≥128 | Custom Product Name, can be set by the host. | | Endpoint | R/W | Staging account endpoint | Y | ≥128 | The endpoint of the AWS account to which the ExpressLink module connects (also see [9.3.2 ExpressLink onboarding states and transitions](elpg-provisioning.md#elpg-provisioning-onboarding-states)). | | RootCA | R/W | AWS root CA | N | ≥4KB | The server root certificate that will be used to authenticate the cloud Endpoint (also see [7.12 Server Root Certificate Update](elpg-ota-updates.md#elpg-server-root-cert)). | | ShadowToken | R/W | ExpressLink | Y | 64 | The default client-token that will be used to mark Device Shadow updates. | | DefenderPeriod | R/W | 0 | Y | ≥8 | The Device Defender upload period in seconds. (0 indicates the service is disabled.) | | HOTAcertificate | R/W | \$1empty\$1 | Y | ≥4KB | Host OTA certificate (see [7.10 Host OTA Signature Verification](elpg-ota-updates.md#elpg-hota-sig-verification)). | | OTAcertificate | R/W | Vendor OTA Certificate | N | ≥4KB | Module OTA certificate. Vendor and Model specific (see [7.5 Module OTA signature verification](elpg-ota-updates.md#elpg-ota-signature-verification)). (Wi-Fi modules only.) | | SSID | R/W | \$1Empty\$1 | Y | 32 | SSID of local router (Wi-Fi modules only). | | Passphrase | W | \$1Empty\$1 | Y | 64 | Passphrase of local router (Wi-Fi modules only). | | APN | R/W | \$1default\$1 | Y | 128 | Access Point Name (Cellular modules only). | The additional configuration parameters in Table 3 are non-persistent. They are re-initialized at power up, and following any reset event. The host processor might have to re-configure them following a reset and (possibly) a *deep sleep* awakening (depending on the implementation). **Table 3 - Configuration dictionary non-persistent keys** | Configuration Parameter | Type | Initial Value | Buff Size | Description | | --- | --- | --- | --- | --- | | QoS | R/W | 0 | 1 | QoS level selected for SEND commands | | Topic1 | R/W | \$1Empty\$1 | ≥128 | Custom defined topic 1 | | Topic2 | R/W | \$1Empty\$1 | | Custom defined topic 2 | | ... | | | | | | Topic | R/W | \$1Empty\$1 | | Custom defined topic MaxTopic | | EnableShadow | R/W | 0 | 1 | 0 - disabled, or 1 - enabled | | Shadow1 | R/W | \$1Empty\$1 | 64 | Custom defined named shadow | | ... | | | | | | Shadow | R/W | \$1Empty\$1 | | Custom defined named shadow | ## 5.1 Data values referenced **5.1.1.1**   Maximum key length is 16 characters A parameter name (key) can be from 1 to 16 characters. **Returns:** **5.1.1.2**   `ERR9 INVALID KEY LENGTH` If a parameter name (key) exceeds 16 characters, the ExpressLink module returns 'ERR9 INVALID KEY LENGTH'. **5.1.1.3**   Valid key characters are 0-9, A-Z, a-z A parameter name (key) may only contain alphanumeric characters. **Returns:** **5.1.1.4**   `ERR10 INVALID KEY NAME` If a non-alphanumeric character is used in a key name, then the ExpressLink module returns 'ERR10 INVALID KEY NAME'. **5.1.1.5**   `ERR11 UNKNOWN KEY` If the parameter name (key) is not found in [Table 2 - Configuration dictionary persistent keys](#elpg-table2) or [Table 3 - Configuration dictionary non-persistent keys](#elpg-table3), then the module returns 'ERR11 UNKNOWN KEY'. **5.1.1.6**   `ERR4 PARAMETER ERROR` If the parameter (value) length exceeds the buffer size as defined in [Table 2 - Configuration dictionary persistent keys](#elpg-table2) or [Table 3 - Configuration dictionary non-persistent keys](#elpg-table3). ## 5.2 Data accessed through the CONF command ### 5.2.1 CONF KEY=*\$1value\$1*   »Assignment« Assign a value to a configuration parameter present in the configuration dictionary. (See [7.11.1 CONF? *\$1certificate\$1 pem*   »Special certificate output formatting option«](elpg-ota-updates.md#elpg-ota-confq-command)).Returns: **5.2.1.1**   `OK{EOL}` If the write is successful, then the module returns 'OK'. Example: ``` AT+CONF Topic1={EOL} # Assign the empty string to Topic 1 OK ``` **5.2.1.2**   `ERR9 INVALID KEY LENGTH` If the key is too long, then the module returns 'INVALID KEY LENGTH'. **5.2.1.3**   `ERR10 INVALID KEY NAME` If the key uses incorrect characters, then the module returns 'INVALID KEY NAME'. **5.2.1.4**   `ERR11 UNKNOWN KEY` If the key is not present in the dictionary, then the module returns 'UNKNOWN KEY'. Example: ``` AT+CONF VERSION=1.0 # Incorrect capitalization ERR11 UNKNOWN KEY # The key is not recognized as spelled ``` **5.2.1.5**   `ERR12 KEY READONLY` Some keys are read-only and cannot be written. If the key cannot be written to, then the module returns 'KEY READONLY' (for example, ThingName, Certificate, About). Example ``` AT+CONF Version=1.0 # Attempt to manually modify the Version parameter ERR12 KEY READONLY ``` **5.2.1.6**   `ERR23 INVALID SIGNATURE` When updating a certificate (for example, Certificate, OTAcertificate, HOTAcertificate) if a required signature verification failed, then the module returns 'INVALID SIGNATURE'. (See [7.11 Host OTA certificate update](elpg-ota-updates.md#elpg-hota-cert-update) for more detail on the signature verification rules that apply to different types of certificates.) ### 5.2.2 CONF? *key*   »Read the value of a configuration parameter« Returns: **5.2.2.1**   `OK {value}` If the read is successful, then the module returns 'OK'. **5.2.2.2**   `ERR9 INVALID KEY LENGTH` If the key is too long, then the module returns 'INVALID KEY LENGTH'. **5.2.2.3**   `ERR10 INVALID KEY NAME` If the key uses incorrect characters, then the module returns 'INVALID KEY NAME'. **5.2.2.4**   `ERR11 UNKNOWN KEY` If the key is not present in the system, then the module returns 'UNKNOWN KEY'. **5.2.2.5**   `ERR13 KEY WRITEONLY` Some keys are write-only and cannot be read. If the key cannot be read, then the module returns 'KEY WRITEONLY'. Example: ``` AT+CONF? Passphrase ERR13 KEY WRITEONLY ```