The present invention relates to a data communication device and a technique effectively applied for a technique of data communication performed between, mainly, an MPU (Micro Processing Unit) and a main storage device or the like.
Methods of performing data communication between integrated circuits are roughly divided into a parallel communication method (parallel link) using a plurality of transmission lines and transmitting data in parallel, and a serial communication method (serial link) using a single transmission line and transmitting data in series. Usually, the parallel link can simultaneously transmit plural data, so that a transmission/reception data amount per unit time is large. However, since it is necessary to suppress a skew of timings of the plural data, the parallel link is generally used, for example, in data communication between the semiconductor integrated circuits having a short transmission line. On the other hand, in the serial link, since only a piece of data can be transmitted/received per unit time, the transmission/reception data amount per unit time is small. However, it is unnecessary to consider the timing skew, so that transmission of long distance is easy. The serial link is mainly used for connecting digital devices such as a VCR (video cassette recorder), a DVD player, a mini-disc recorder, a set-top box, and the like.
An example of the parallel link is disclosed in “JEDEC standard 79, Double Data Rate (DDR) SDRAM specification” (hereinbelow, called Literature 1). An example of the serial link is disclosed in “Architecture of IEEE 1394”, Interface, July, 1999 (hereinbelow, called Literature 2).