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4.16. Two-wire serial bus interface, SBCon

Two custom two-wire serial bus interfaces (SBCon 0 and SBCon 1) are implemented in the Southbridge.

SBCon 0 provides access to:

  • the serial EEPROM on PISMO static memory expansion boards

  • the Maxim DS1338 RTC on the baseboard.

SBCon 1 provides access to:

  • the Digital Data Channel (DDC) of the external display connected to the DVI connector on the rear panel.

Table 4.45. Serial bus implementation
PropertyValue
Location Southbridge
Memory base addressSBCon 0: 0x10002000 SBCon 1: 0x10016000
Interrupt
DMA
Release versionCustom logic
Reference documentation

The registered device addresses are listed in Table 4.46

Table 4.46. Serial interface device addresses
DeviceWrite addressRead addressDescription
PISMO (static memory module)0xA20xA3Identifies the type of memory on the board and how it is configured.
TOY (DS1338 RTC)0xD00xD1Reads time data and writes control data to the RTC.
DVI (external display)display dependantdisplay dependantReads external display capabilities at the DVI connector. Can control display settings of E-DDC displays.

The registers listed in Table 4.47 and Table 4.48 control the serial bus interfaces.

Table 4.47. SBCon 0 serial bus register
AddressNameAccessDescription
0x10002000SB_CONTROLRead

Read serial control bits:

Bit [0] is SCL

Bit [1] is SDA

0x10002000SB_CONTROLSWrite

Set serial control bits:

Bit [0] is SCL

Bit [1] is SDA

0x10002004SB_CONTROLCWrite

Clear serial control bits:

Bit [0] is SCL

Bit [1] is SDA


Table 4.48. SBCon 1 serial bus register
AddressNameAccessDescription
0x10016000SB_CONTROLRead

Read serial control bits:

Bit [0] is SCL

Bit [1] is SDA

0x10016000SB_CONTROLSWrite

Set serial control bits:

Bit [0] is SCL

Bit [1] is SDA

0x10016004SB_CONTROLCWrite

Clear serial control bits:

Bit [0] is SCL

Bit [1] is SDA


Note

SDA is an open-collector signal that is used for sending and receiving data. Set the output (sending) value HIGH before reading the current value.

Software must manipulate the SCL and SDA bits directly to access the data in the three devices. See the \firmware\examples directory on the CD for example code for reading the EEPROM that is on the memory expansion board.

Table 4.49. Serial bus device addresses
DeviceWrite addressRead address
Static expansion EEPROM (PISMO)0xA20xA3
Time-of-year clock (TOY)0xD00xD1
External displaydisplay dependantdisplay dependant

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