SPRUHM9H October 2014 – May 2024 TMS320F28075 , TMS320F28075-Q1 , TMS320F28076
The EMIF supports the extended wait mode. This is a mode that the external asynchronous device can assert control over the length of the strobe period. The extended wait mode can be entered by setting the EW bit in the asynchronous n configuration register (ASYNC_CSn_CR (n = 2, 3, or 4). When this bit is set, the EMIF monitors the EM1WAIT pin to determine if the attached device wishes to extend the strobe period of the current access cycle beyond the programmed number of clock cycles.
When the EMIF detects that the EM1WAIT pin has been asserted, the EMIF begins inserting extra strobe cycles into the operation until the EM1WAIT pin is deactivated by the external device. The EMIF then returns to the last cycle of the programmed strobe period and the operation proceeds as usual from this point. Refer to the device data sheet for details on the timing requirements of the EM1WAIT signal.
The EM1WAIT pin cannot be used to extend the strobe period indefinitely. The programmable MAX_EXT_WAIT field in the asynchronous wait cycle configuration register (AWCC) determines the maximum number of EM1CLK cycles the strobe period can be extended beyond the programmed length. When the counter expires, the EMIF proceeds to the hold period of the operation regardless of the state of the EM1WAIT pin. The EMIF can also generate an interrupt upon expiration of this counter. See Section 23.2.9.1 for details on enabling this interrupt.
For the EMIF to function properly in the extended wait mode, the WPn bit of AWCC must be programmed to match the polarity of the EM1WAIT pin. In the reset state of 1, the EMIF inserts wait cycles when the EM1WAIT pin is sampled high. When set to 0, the EMIF inserts wait cycles only when EM1WAIT is sampled low. This programmability allows for a glueless connection to larger variety of asynchronous devices.
Finally, a restriction is placed on the strobe period timing parameters when operating in extended wait mode. Specifically, the sum of the W_SETUP and W_STROBE fields must be greater than four, and the sum of the R_SETUP and R_STROBE fields must be greater than four for the EMIF to recognize the EM1WAIT pin has been asserted. The W_SETUP, W_STROBE, R_SETUP, and R_STROBE fields are in ASYNC_CSn_CR.