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Standard Serial Interface Protocol Description 5.4.2 1/8 Controller Response Protocol (10072 Controller Only) The 1/8 VGA controller responds to Images the same as in section 4.2 accept the negative response contains an added byte (Error Code) to report the reason the Image received a negative response. The negative response format would appear as follows: Field Description Packet Field # Byte #/ Field NAK Message # Error Code Message Checksum Carriage Return Line Feed 1 2 3 4 5 6 1 1 1 1 1 1 Table 5.4.2 Where: 1/8 Controller Negative Response Message Packet Format 1. NAK = ASCII acknowledgment character; 15 (Hex) 2. Message # = Message number of the previously transmitted host message package, 0-255 possibilities. 3. Error Code = Checksum error Buffer full controller busy reserved for debugging and future use. 4. Message Checksum = Equals the least significant 8 bits of the summation of all elements contained in message packet fields 1 and 2. 5. Carriage return = ASCII carriage return, or 0D in hexadecimal. 6. Line feed = ASCII line Feed, or 0A in hexadecimal. 5.4.3 Maximum Number of 1/8 VGA Image Storage Capacity (10120 Controller Only) As indicated in the “” references in table 5.4.1, the 1/8 VGA 10120 controller module can store several images, messages or pages of data for the respective display number assigned to the controller module. To maximize the amount of messages to be stored in the controller module, the controller uses a dynamic memory allocation method. Each message type for each display within a given message (or “Page”) is allocated a fixed memory space, based on the message type for the given display. The dynamic memory allocation firmware uses a “link list” to place each display image in consecutive section of the controller RAM memory. The following memory space allocations are assigned to the available message types: # Message Type Field #4 Command Designation(s) Fixed Memory Space Allocation 1. Full Screen Text “A” 833 Bytes / Display image 2. Full Screen Graphic “B” 4814 Bytes / Display image 3. Partial Screen Text, Dynamic “N”, “F” and “H” 55 Bytes / Display image Update Text, Flashing Text 4. Partial Screen Graphic “U” 3014 Bytes / Display image 5 Dyanamic Update Partial Screen Graphic “G” 494 Bytes / Display image Table 5.4.3: Controller Memory Space Allocations for Different Types of Message Data Standard Serial Communication Interface Description, © 1998-2002 Kent Displays Inc., doc. # 25016 Revision T, Page 25 of 52
Standard Serial Interface Protocol Description As indicated previously, the 10120, 1/8 VGA controller module will load display image data into memory sequentially, into the next available memory location. Since the controller has a finite amount of memory storage capacity, the interface software (“1/8VGASoft”, or equivalent) will need to either keep track of the amount of bytes used in the respective controller address prior to transmitting, or the controller will need to be “asked” the amount of available memory for an additional display message storage. For instance, the maximum amount of message data that can be loaded into a 1/8 VGA controller can not exceed 43,817 bytes. The following items pertain to maximizing the number of complete messages stored by a 1/8 VGA, 10120 controller module: o To maximize the number complete messages to be loaded into a controller module, use textbased messages (full, partial, flashing or partial screen text dynamic update) whenever possible. For instance, the 1/8 VGA controller can store only 9 complete full screen graphic messages {4814 [bytes/message] x 9 [messages] = 43,326 [bytes]}, whereas the same controller can store 52 complete full screen text based message {833 [bytes/message] x 52 [messages] = 43,316 [bytes]}, which is less than the 43,817 bytes capacity. Additional message storage capacity can be obtained if partial screen text images are used whenever possible. 5.4.3.1 Controlling and Determining the Message Count (10120 Controller Only) The following application commands are available to the user to enable the interface to query (or “ask”) the 1/8 VGA controller the amount of available RAM memory left for additional message storage, and to enable the user to clear existing memory in the event the controller dynamic message storage algorithm becomes fragmented. # (Field #4) (Field #5) (Field #6) # Cmd. Content Byte Typical Byte Message Description Designation Count Content Count 1 "M" N/A 0 N/A 0 Output "M"essage storage availability from controller. Host will receive message f/controller after positive response is received. 2 “>” (3e in Hex) N/A 0 N/A 0 Clear All Previously Received Message Data (overides any previous Message trigger or Automatic cycle command received). Table 5.4.4: Additional Controller Memory Allocation/Query Commands As indicated from the table above, the interface will receive a message like the following example after the 320x80 controller receives a “M” command: RAM Bytes Used = 0791 RAM Bytes Available = A398 RAM Fragmented = 0000 The quantities provided on each line after the introductory text is output in ASCCI hexadecimal format. As illustrated in the example above, the given 1/8 VGA controller currently has 0791 (1937 10 ) bytes occupied with user message data, has A398 (41,880 10 ) bytes available for additional message storage, and has 0 bytes wasted due to fragmentation of the message data. On current 1/8 VGA controller designs, message data fragmentation will only occur if the user changes an existing message (for a given message and display number) from one message type, to another as indicated in table 5.4.3. If the amount of RAM space, which is fragmented, becomes excessive, the user (or the “interface”) may wish to output a “Clear All Previously Received Message Data” command (“>” Standard Serial Communication Interface Description, © 1998-2002 Kent Displays Inc., doc. # 25016 Revision T, Page 26 of 52
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