SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
There are I/O cells specially intended for the MLB 6-pin interface. These are low-voltage differential signaling (LVDS) I/O cells with controls, which reside in several registers of the CTRL_MODULE_CORE. In addition, there is also a bandgap cell which provides a reference voltage to the LVDS IOs associated with the MLB interface. Without this reference voltage these differential receivers and transmitters cannot function properly. The LVDS IOs must be used only when 6-pin mode is selected. If this is done the six MLB signals are available on the following pads:
Figure 24-208 shows the LVDS IOs used when 6-pin MLB mode is selected, their controls from CTRL_MODULE_CORE, the MLB bandgap cell and details regarding the multiplexing scheme when 3-pin mode is used.
3-pin mode is used when the MLB_MLBC0[5] MLBPEN bit is set to 0x0. When this bit is set to 0x1 a 6-pin mode is used. In case of 3-pin mode an additional step must be performed to be the MLB signals (mlb_sig, mlb_dat and mlb_clk) available on the device pads. These signals are multiplexed along with other device signals on the following pads:
For more information about signal multiplexing see Pad Configuration Registers in Control Module and also table "Multiplexing Characteristics" of the device Data Manual.
The MLB bandgap cell is intended to provide a stable reference voltage to the LVDS IOs across voltage and temperature variations. This cell is powered when the CTRL_CORE_MLB_CLK_BG_CTRL[1] BG_PWRDN bit is set to 0x0. When powerd the MLB bandgap cell provides its reference voltage to the LVDS IOs which is a prerequisite for their proper working. The CTRL_CORE_MLB_CLK_BG_CTRL[7:2] BG_TRIM bit field is used for trimming the reference voltage generated by the MLB bandgap cell. When reading the BG_TRIM bit field and if its value is 0x0 it is recommended to write 0x20 to this bit field. In all other cases (BG_TRIM != 0x0) software write to the BG_TRIM bit field is not recommended.
The MLB differential clock receiver is enabled when the CTRL_CORE_MLB_CLK_BG_CTRL[0] CLK_PWRDN bit is set to 0x0. The CTRL_CORE_MLB_CLK_BG_CTRL[16] T_HYSTERISIS_EN bit is used to enable/disable the hysteresis for the MLB differential clock receiver. A value of 0x1 enables the hysteresis and 0x0 disables it.
The power of the MLB differential receivers and transmitters can be switched ON and OFF using the PWRDNRX and PWRDNTX bits, respectively. A value of 0x0 powers up and a value of 0x1 powers down the receivers and transmitters. The bits are the following:
There are also CTRL_MODULE_CORE bits to remove the skew effect of the mlbp_sig_p/mlbp_sig_n and mlbp_dat_p/mlbp_dat_n signals caused by difference in the input impedance between "_p" and "_n" lines of the receivers. The bits for doing this are the following:
The MLB differential transmitters have also controls for trimming their output impedance and for enabling/disabling their internal pull resistors. Setting to 0x1 the CTRL_CORE_MLB_SIG_IO_CTRL[3] SIG_EN_EXT_RES bit enables the internal pull resistors of the mlbp_sig_p/mlbp_sig_n transmitter. Setting to 0x1 the CTRL_CORE_MLB_DAT_IO_CTRL[3] DAT_EN_EXT_RES bit enables the internal pull resistors of the mlbp_dat_p/mlbp_dat_n transmitter. If the internal pull resistors are disabled external on-board pull resistors must be provided.
In addition, when 3-pin mode is used, there is no need to configure any of the previously described CTRL_MODULE_CORE registers associated with the MLB LVDS IOs. In this case a MUXMODE configuration is required.