USB Communication

This page has not been completed. Parts may be missing or reorganized before completed. Information is provided as-is and may have errors.

If you have any documentation or have played around with the USB communication for the Prizm, please contribute your findings by editing this page. Thank you!

The Prizm includes a mini-B female USB connector. Over a USB 2.0 connection, users can manage the files on the calculator, mirror the calculator screen to a computer or certain Casio projectors, and update the Operating System. Of these operations, only file management can be done without the use of additional software or drivers, as in this mode, the calculator registers as a Mass-Storage Device. This allows for transferring files even in operating systems other than Microsoft Windows.

The screen mirroring functionality requires that Screen Receiver, which is freeware software from Casio available for Windows and Mac OS X, be installed on the computer. The OS update functionality requires a OS updater to be running on the computer.

The calculator can be used normally, without entering any of the USB modes, while a powered USB cable is connected. This is done by pressing EXIT on the USB mode selection screen. When powered over USB, the calculator takes no or very little battery power. It doesn’t support battery charging.

Pressing EXIT on the USB mode selection screen and going into the System app is also necessary to perform a OS update, as instructed by the updater.

Mass Storage mode #

In this mode, which can be selected by pressing F1 on the dialog that appears when connecting the USB cable, the calculator emulates a USB Flash Drive. Before initiating the connection, the OS serializes all the data in the Main Memory to the @MainMem folder in Storage Memory, which is not visible from the file lists displayed by the OS on the calculator. After terminating the USB connection, the calculator translates the contents of the @MainMem folder back into the Main Memory, replacing the existing ones (so that if the @MainMem folder is deleted, all data in the Main Memory is deleted) and placing unrecognized files in a folder named “SAVE-F”. In fact, this process is detailed starting on page 13-5 of the Prizm’s Software Manual, including the file names associated with each Main Memory item.

The computer should never be used to format the Storage Memory. Doing so will prevent the calculator from being used, as it will keep displaying “File System ERROR” - presumably due to not being able to mount the specially-formatted FAT file system in Flash. The only way to get out of this situation is to perform a general reset of the calculator, making the OS format the file system in its own terms.

Screen Receiver mode #

The calculator has two Screen Receiver modes: one for connection to a Windows XP computer and another for connection to other (more recent) operating systems. As explained above, both need the Screen Receiver software to be installed on the computer. Certain Storage Memory operations are not available in this mode.

Please see Screen_Receiver for more details.

Projector mode #

Not much is known about this mode, mainly because it requires the use of specific hardware - the Casio projectors. It is known that, in earlier OS versions at least, this mode had certain problems that caused instability on the calculator, including System ERRORs. The Prizm’s software manual even includes some suggestive paragraphs on troubleshooting this mode, including instructions for reconnecting the USB cable and power-cycling the projector. This gives the impression that Casio engineers did not have much access to testing hardware, or that the decision to support the Projector mode was taken very late in the development process, not giving enough time for proper testing and error-proofing of the code.

OS Update mode #

This is a special mode that waits for a OS Updater to issue special commands over USB, and implements Protocol 7 at least partially.

Protocol #

The Prizm uses the MSD USB protocol for Drive mode, Screen Receive, and OS Updates (both modes). For the extra data, it uses UFI bulk-mode data methods.

MSD CBW Description #

Bit 7 6 5 4 3 2 1 0
0-3 bCBWSignature
4-7 dCBWTag
8-11 dCBWDataTransferLength
12 bmCBWFlags
13 Reserved (0) bCBWLUN
14 Reserved (0) bCBWCBLength
15-30 CBWCB
  • dCBWSignature - Always 0x43425355 in little endian. Indicates a CBW.
  • dCBWTag - A 4 byte tag sent by the host, echoed back by the peripheral in a CSW.
  • dCBWDataTransferLength - Amount of bytes, in little endian, expected to be sent/received on a bulk pipe directly after sending the packet.
  • bmCBWFlags - 0x00 if sending host to device, 0x80 if device to host. Ignored if dCBWDataTransferLength is 0.
  • bCBWLUN - Set to 0.
  • bCBWCBLength - Length of usable data in CBWCB. Doesn’t mean packet size is different!
  • CBWCB - Command block to be executed. For the Prizm, this is a UFI command block.

MSD CSW Description #

Bit 7 6 5 4 3 2 1 0
0-3 dCSWSignature
4-7 dCSWTag
8-11 dCSWDataResidue
12 bCSWStatus
  • dCSWSignature - Always 0x53425355 in little endian. Indicates a CSW.
  • dCSWTag - Set to the dCBWTag of the received CBW.
  • dCSWDataResidue - When receiving data from the host, this is the difference between the amount of data expected in dCBWDataTransferLength and the actual amount of data processed. For sending, it is the difference between dCBWDataTransferLength and actual bytes sent.
  • bCSWStatus - Indicates the success or failure. Responses are below
Value Description
0x00 Command Passed
0x01 Command Failed
0x02 Phase Error
0x03 and 0x04 Reserved (Obsolete)
0x05 to 0xFF Reserved

If there is an error, you should perform a phase recovery.

MSD UFI Command Block Description #

Bit 7 6 5 4 3 2 1 0
0 Operation Code
1 Logic Unit Number Reserved
2 (MSB) Logical Block Address
5 (LSB)
6 Reserved
7 (MSB) Transfer or Parameter list or Allocation Length (usually allocation length)
8 (LSB)
9 Reserved
10 Reserved
11 Reserved

MSD UFI Extended Command Block Description #

Bit 7 6 5 4 3 2 1 0
0 Operation Code
1 Logic Unit Number Reserved
2 (MSB) Logical Block Address
5 (LSB)
6 (MSB) Transfer or Parameter list or Allocation Length (usually allocation length)
9 (LSB)
10 Reserved
11 Reserved

Prizm UFI Commands #

ID Name Parameters Returns Comments
0xC0 Poll todo The prizm returns a 0xD0 response. Todo. Basically used to see if the Prizm is done processing the last sent data and is ready for more, and also checks to see if the Prizm wants to send something.

0xC0 #

Since the peripheral cannot initiate a data send on its own, the Prizm gets polled constantly to check for any activity. Here is the packet layout:


Custom return data:

D0 00 00 00 00 00 00 SS SS 00 AA AA 00 00 00 00

  • SS SS - Amount of bytes as big endian that the Prizm wants to send
  • AA AA - Activity status of the Prizm. If value is not 10 00, then the Prizm is busy and cannot accept more data.

0xC1 #

Receives data. Should be sent if 0xC0 command revealed that the Prizm wants to send stuff. Syntax:

C1 00 00 00 00 00 SS SS

  • SS SS - Amount of bytes to be sent.

Once this is sent, the Prizm sends raw data.

0xC2 #

This command is used to send raw data to the Prizm. It seems the first byte of the raw data is not part of the data. The raw data usually is made up of character-encoded hex at the start. Command syntax:

C2 00 00 00 00 00 SS SS

  • SS SS - Amount of bytes to be sent.

Once this is sent, send the raw data directly after. Poll before sending more.

Protocol 7 #

Protocol 7 is the method for communicating to Casio calcs over IO or USB. The commands are sent in special command packets sent to the prizm as raw data after sending a 0xC2 command as an MSD UFI command. Confusing? Indeed. Below is the table showing you how the raw data sent to the Prizm from the 0xC2 UFI commands is read:

Byte Field Name Desciption Values
1 Type The basic purpose of the packet 0x00 to 0x1F
2 Subtype The specific function of the packet “00” to “57”
1 Extended Decides if data size and data field follow ‘0’ - no; ‘1’ - yes
(4, if extended) Data size Size of data field “0000” to “FFFF”
(n, if extended) Data Additional data related to packet function
2 Checksum Checksum for integrity check “00” to “FF”

The protocol on the Prizm is not exposed in all modes. Currently, USB Drive mode ignores Protocol 7 packets, but not the UFI packets. In screen receiver, there is a role swap and the packet structure is different. The only mode known to follow this is OS Update mode.

Credits #

Simon Lother and Andreas Bertheussen for Protocol 7 info. PDF released under Attribution-NonCommercial-NoDerivs 3.0 Unported (CC BY-NC-ND 3.0) license, located here.