The following section describes the states in the state machine in more detail.
stm_idle: This is the idle state. In this state, the counter, count_gxb_pwrdn is used to measure how long the gxb_pwrdn_in signal is asserted. When the gxb_pwrdn_in signal has been asserted for 1 µs, the idle state transits to the next state, the stm_gxb_pwrdn.
stm_gxb_pwrdn:This is the ALTGX transceiver's powerdown state. During this state, the gxb_powerdown output signal is asserted. When the gxb_pwrdn_in signal is deasserted, the state transits to the next, the stm_pll_locked.
stm_pll_locked: This is the state that detects the pll_locked signal. During this state, the gxb_powerdown output signal is deasserted. When the transceiver is locked, the pll_locked signal is asserted, and once it is detected, the state transits to the next, the stm_tx_digitalreset.
stm_tx_digitalreset: This is the transmitter's digital reset state. In this state, the tx_digitalreset output signal is deasserted. When the counter, count_rx_analogreset has counted two parallel clock cycles, the state transits to the next, the stm_rx_analogreset.
stm_rx_analogreset:This is the receiver's analog reset state. In this state, the rx_analogreset output signal is deasserted. When the receiver frequency is locked, the rx_freqlocked signal is asserted, and the state transits to the next, the stm_rx_freqlocked.
stm_rx_freqlocked:In this state, the counter, count_rx_digitalreset counts up till 4 µs, and then the state transits to the next, the stm_rx_digitalreset.
stm_rx_digitalreset: This is the receiver's digital reset state. In this state, the rx_digitalreset output signal is deasserted.
Points to note:
- Whenever the gxb_pwrdn_in signal is asserted for 1 µs, the state machine returns to the stm_gxb_pwrdnstate.
- Whenever the pll_locked signal is deasserted, the state machine returns to the stm_pll_lockedstate.
- Whenever the rx_freqlocked signal is deasserted, the state machine returns to the stm_rx_analogreset state.
For more information about instantiating TSE with an external ALTGX, please refer to the following design example:
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