Messages (Requests, Responses, Notifications, And Files); About Messages - Magtek DynaFlex II Go Programmer's Manual

3 - Messages (Requests, Responses, Notifications, and Files)

3 Messages (Requests, Responses, Notifications, and Files)
This section describes the general format of messages exchanged between hosts and devices that are using
the common MMS message framework.
Documentation about the specific messages supported by a given device is provided in section 6
Commands.
3.1

About Messages

The host and the device communicate with each other by exchanging blocks of data called Messages,
which are standardized wrappers containing a payload that is either a command Request, a command
Response, an unsolicited Notification, or a File. For example, the host may send a command request
message to the device to change a configuration setting, and the device may send a command response
message to indicate the command was successful; when a cardholder inserts a card, the device may send a
notification message to the host that a cardholder has initiated a transaction; the host may send the device
a file message to load firmware.
Messages can be nested. For example, a top-level secure wrapper request from the host to the device may
contain an encrypted or signed command request for the device to unpack, validate, and execute.
Requests and Responses. Requests and responses are two of the message payload types the host and
device exchange inside messages. The combination of a message that contains a request payload and a
message that contains the corresponding response payload is referred to generally in this document as a
Command. The device can only service one command request at a time, and sends each command
response within a pre-determined finite amount of time after receiving the request. After sending a
command request, the host must wait until the device returns a response before sending another request,
or until the request is unanswered after a reasonable host-defined timeout period passes.
Notifications. Notifications are a message payload type the host and device exchange inside messages.
The device sends notification messages to the host if the device's state changes or if an external event
occurs, such as a cardholder inserting a card. The device can send a notification at any time, and does not
expect a response or any specific action from the host. By default, the device sends all notifications to the
USB interface. To configure the device to send notifications on additional connections, use Command
0x1F02 - Set Notification Subscriptions.
Data Files. Data Files are a message payload type the host and device exchange inside messages. The
device handles them as a stream, in that it begins storing the payload of the message before it has received
the final packet of the message, allowing for much larger payloads than standard requests. This is made
possible by restricting the function of the message to just transferring a file, which means restricting the
message payload to primitive data only; it can not contain composed TLV data objects.
Regardless of connection type, all MMS devices use the same schema for sending and receiving
messages, which is documented in section 3.2 Message Format. For information about transmitting and
receiving messages using specific connection types, which involves following connection-specific rules
for breaking messages down into transmittable Message Streams, see section 2 Connection Types.
DynaFlex II Go| Secure Card Reader | Programmer's Manual (COMMANDS)
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