Table 1. Register Map Differences
|Register Name.Bit||Address||Bit Name||DS2155||DS21458||Comments|
|CCR1.3||70h||DICAI||X||--||Disable Idle Code Auto Increment - Selects/deselects the auto-increment feature for the transmit and receive idle code array address register, this function is not available in the DS21458|
|CCR1.7||70h||MCLKS||X||--||MCLK Select, allows the user to select either TSYSCLK or MCLK as the master clock, this function is not available in the DS21458|
|CCR3.6||72h||INTDIS||X||--||Interrupt Disable, allows the user to disable all interrupts regardless of the Interrupt Mask Register settings, this function is not available in the DS21458.|
|CCR3.7||72h||TMSS||X||--||Transmit Multi-frame Sync Source, allows the users to select the framer or TSYNC pin as the source of the multi-frame sync, this feature is not available on the DS21458.|
|LBCR.7||4Ah||LTS||--||X||LIUC/TPD Pin Function Select, this pin selects the function of the LIUC/TPD pin and should always be set to a 1 in the DS21458. This bit does not exist in the DS2155 memory map.|
|PSA1||F1h||--||--||X||Pulse Shape Adjustment Register 1 - Allows the user to adjust the transmit pulse waveform, this register is not available on the DS2155.|
|PSA2||F2h||--||--||X||Pulse Shape Adjustment Register 2 - Allows the user to adjust the transmit pulse waveform, this register is not available on the DS2155.|
|IDR||0Fh||--||X||X||Device Identification Register - This read only register displays the Device ID and Chip Revision of the given device and the contents will depend on which part or revision is used.|
The DS2155 has a single MCLK pin, while the DS21458 has two MCLK pins called MCLK1 and MCLK2. These two pins can be driven from a common source on the DS21458.
The DS2155 has an XTALD pin to allow the option of using a quartz crystal applied across the MCLK and XTALD pins. The DS21458 does not support this and therefore has no XTALD pin.
The 8xCLK pin is also not available on the DS21458. This pin is an 8x clock output pin on the DS2155 but has been removed on the DS21458.
The DS21458 has two more address pins, A8 and A9 that do not exist on the DS2155. These address pins are used to select one of the four ports.
The DS2155 has four generic user output pins that do not exist on the DS21458. These pins are UOP0, UOP1, UOP2 and UOP3.
The LIUC pin, which is used to separate the Line Interface Unit (LIU) and the Framer on the DS2155, is called the Transmit Power Down (TPD) pin on the DS21458. The user has limited access to the clock and data signals between the framer and the LIU on the DS21458 and the LIUC pin is not required. The TPD functionality is only available on the DS2155 via the register bit TPD located in the LIC1 register. With the reduced access to signals between the LIU and the Framer, the following pins are not present on the DS21458: TPOSI, TNEGI, TCLKI, RPOSI, RNEGI and RCLKI.