This chip has two 336x243 arrays. One is the sensing area exposed to light. Another one is the storage area protected from light. Light produces charges that accumulate in the sensing array. The content of the sensing array is then moved to the storage area one line at a time.
Light spoiles the image in the sensing array during the transfer, so it needs to be fast.
In the transfer all the carges from the sensing area are removed. Thus the exposure is time between two successive transfers. Once the image is in the storage area it can be moved out of the chip pixel by pixel and it takes much longer which is ok, because now light does not affect those charges. SRG can not go higher 7 MHz, others are limited by 4 MHz. Very low frequencies will result in image smearing.