Patent Publication Number: US-2018052784-A1

Title: Semiconductor device and electronic device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2012-287269, filed on Dec. 28, 2012, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     The present invention relates to a semiconductor device and electronic device and, for example, to a semiconductor device and electronic device which are suitable for car navigation systems or the like. 
     Car navigation systems including multiple monitors have been developed in recent years. Such a car navigation system controls image display on the monitors on the basis of a program or various types of data stored in a memory. 
     Japanese Unexamined Patent Application Publication No. 2008-171432 discloses a configuration that synchronously controls multiple memory controllers coupled to memories using a synchronous circuit. Japanese Unexamined Patent Application Publication No. 2009-128313 discloses the configuration of a car navigation system. 
     SUMMARY 
     The inventors have found various problems in the development of a semiconductor device used in an electronic device, such as a car navigation system. Embodiments disclosed in the present application provide semiconductor devices which are suitable for car navigation systems or the like. 
     Other problems and novel features will be apparent from the description of the present specification and the accompanying drawings. 
     A semiconductor device according to one embodiment includes a selector configured to select between a memory interface and an inter-device interface in accordance with an operation mode of the semiconductor device and to couple the selected interface to terminals. 
     According to the one embodiment, it is possible to provide a good-quality semiconductor device which is suitable for electronic devices, such as car navigation systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, advantages and features will be more apparent from the following description of certain embodiments taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram showing an example configuration of an electronic device  100  according to the first embodiment; 
         FIG. 2  is a block diagram showing an example configuration of the semiconductor device SD according to the first comparative example; 
         FIG. 3  is a block diagram showing an example configuration of the semiconductor device SD according to the second comparative example; 
         FIG. 4  is a block diagram showing an example configuration of the semiconductor device SD according to the third comparative example; 
         FIG. 5  is a block diagram showing an example configuration of the semiconductor device SD according to the first embodiment; 
         FIG. 6  is a block diagram of the semiconductor chip SC 1  according to the first embodiment which is placed in the single mode; 
         FIG. 7  is a circuit diagram showing the internal configuration of the memory interface MIF 1 ; 
         FIG. 8  is a block diagram showing the internal configuration of the inter-chip interface ICIF; 
         FIG. 9  is a plan view showing an example of disposition of the terminals T of the semiconductor chip SC 1 ; 
         FIG. 10  is a diagram showing assignment of signals to the terminals disposed in the broken line frame (x=1 to 5 and y=1 to 5) of  FIG. 9 ; 
         FIG. 11  is a block diagram showing an example configuration of the semiconductor device SD according to the second embodiment; and 
         FIG. 12  is a block diagram of the semiconductor chip SC 1  according to the second embodiment which is placed in the single mode. 
     
    
    
     DETAILED DESCRIPTION 
     Now, specific embodiments will be described in detail with reference to the accompanying drawings. However, the embodiments are not restrictive. To clarify the description, simplified descriptions or drawings are shown as necessary. 
     First Embodiment 
     Configuration of Electronic Device 
     First, referring to  FIG. 1 , there will be described the configuration of an electronic device to which a semiconductor device according to a first embodiment is applied.  FIG. 1  is a block diagram showing an example configuration of an electronic device  100  according to the first embodiment. Hereafter, there will be described an example in which the electronic device  100  is a car navigation system to be mounted on an automobile. As shown in  FIG. 1 , the electronic device  100  includes a semiconductor device SD, a monitor  10 , a memory  20 , a digital versatile disc (DVD) drive  30 , a camera  40 , a storage device  50 , and a global positioning system (GPS) module  60 . 
     The semiconductor device SD controls the monitor  10 , the memory  20 , the DVD drive  30 , the camera  40 , the storage device  50 , and the GPS module  60 . The semiconductor device SD shown in  FIG. 1  may include a single chip or multiple chips. For example, if the monitor  10  includes multiple monitors, the semiconductor device SD also includes multiple chips. The internal configuration of the semiconductor device SD according to the first embodiment will be described in detail with reference to  FIG. 5  later. 
     The monitor  10  is a display device, such as a liquid crystal display (LCD) or organic light-emitting diode (OLED) display. The monitor  10  displays navigation images, as well as images stored in a DVD inserted into the DVD drive  30 , images captured by the camera  40 , or the like. Switching of the image displayed by the monitor  10  is controlled by the semiconductor device SD. If the monitor  10  includes multiple monitors, it is possible, for example, to display navigation images to the monitor of the driver&#39;s seat and to display images (e.g., movie) of a DVD to the monitor of the passenger seat or rear seat. That is, the multiple monitors can display different images. 
     The memory (external memory)  20  is storing programs and data used by the semiconductor device SD. Often used as the memory  20  is a dynamic random access memory (DRAM), which is a volatile memory, where stored data is erased when power is shut off. Of course, a non-volatile memory, where stored data is held when power is shut off, may be used as the memory  20 . 
     The DVD drive  30  reads images stored in a DVD. The images of a DVD inserted into the DVD drive  30  are output from the monitor  10 . 
     The camera  40  is, for example, a so-called rear view camera, which is mounted on the rear of an automobile. The camera  40  captures images of the rear of an automobile, which becomes a blind spot from the driver&#39;s seat when the automobile moves back. The images captured by the camera  40  are output from the monitor  10 . For example, while an automobile moves back (is placed in reverse gear), images captured by the camera  40  are displayed on the monitor  10  of the driver&#39;s seat. 
     The storage device  50  is preferably a mass-storage device, such as a hard disk, and is storing navigation images (map information). 
     The GPS module  60  includes an antenna, an RF circuit, and a base-band circuit. Based on position information received from an artificial satellite, the GPS module  60  outputs the current position of the automobile to the semiconductor device SD. 
     Configuration of Semiconductor Device According to First Comparative Example 
     Next, referring to  FIG. 2 , there will be described a semiconductor device SD according to a first comparative example examined by the inventors.  FIG. 2  is a block diagram showing an example configuration of the semiconductor device SD according to the first comparative example.  FIG. 2  shows the internal configuration of the semiconductor device SD according to the first comparative example, as well as four monitors,  10   a  to  10   d , and four memories,  20   a  to  20   d . The four monitors,  10   a  to  10   d , correspond to the monitor  10  of  FIG. 1 , and the four memories,  20   a  to  20   d , correspond to the memory  20  of  FIG. 1 . In an example of  FIG. 2 , all the memories,  20   a  to  20   d , are 32-bit bus width double-data-rate synchronous dynamic random access memories (DDR SDRAMs). 
     As shown in  FIG. 2 , the semiconductor device SD according to the first comparative example includes four semiconductor chips, SC 11  to SC 14 . Since the four semiconductor chips, SC 11  to SC 14 , have similar configurations, only the semiconductor chip SC 11  will be described. 
     As shown in  FIG. 2 , the semiconductor chip SC 11  includes a central processing unit (CPU), a graphics processing unit GPU, a display control unit DC, a memory controller MC, a memory interface MIF, and an internal bus IB. The CPU, the graphics processing unit GPU, the display control unit DC, and the memory controller MC are coupled together through the internal bus IB. 
     The CPU accesses the memory  20   a  through the memory controller MC and the memory interface MIF. The CPU requests the display control unit DC to, for example, start displaying images on the monitor  10   a  or change the displayed image to another. 
     The graphics processing unit GPU is an operation circuit specialized in graphics rendering. Images rendered by the graphics processing unit GPU are displayed on the monitor  10   a  through the display control unit DC. 
     The memory controller MC transmits a data signal dq and a control signal ctr to the memory interface MIF. The memory controller MC also transmits a data signal dq received from the memory interface MIF to the CPU or graphics processing unit GPU. In an example of  FIG. 2 , the memory  20   a  is 32-bit bus width DDR SDRAM and therefore the memory controller MC is composed of a DDR SDRAM bus state controller (DBSC) for a 32-bit bus width DDR SDRAM. 
     The memory interface MIF transmits the control signal ctr and data signal dq received from the memory controller MC to the memory  20   a . The memory interface MIF also transmits a control signal ctr and a data signal dq received from the memory  20   a  to the memory controller MC. In the example of  FIG. 2 , the memory  20   a  and the memory interface MIF are coupled together through a 32-bit data signal bus and a 30-bit control signal bus. 
     As shown in  FIG. 2 , in the semiconductor device SD according to the first comparative example, the monitor  10   a  and the memory  20   a  are coupled to the semiconductor chip SC 11 . Similarly, the monitor  10   b  and the memory  20   b  are coupled to the semiconductor chip SC 12 ; the monitor  10   c  and the memory  20   c  to the semiconductor chip SC 13 ; and the monitor  10   d  and the memory  20   d  to the semiconductor chip SC 14 . That is, a single monitor and a single memory are coupled to a single semiconductor chip. For this reason, the semiconductor device SD has a problem of an increased implementation area. 
     Configuration of Semiconductor Device According to Second Comparative Example 
     Next, referring to  FIG. 3 , there will be described a semiconductor device SD according to a second comparative example examined by the inventors.  FIG. 3  is a block diagram showing an example configuration of the semiconductor device SD according to the second comparative example. As with  FIG. 2 ,  FIG. 3  shows the internal configuration of the semiconductor device SD according to the second comparative example, as well as four monitors,  10   a  to  10   d , and four memories,  20   a  to  20   d . The four monitors,  10   a  to  10   d , correspond to the monitor  10  of  FIG. 1 , and the four memories,  20   a  to  20   d , correspond to the memory  20  of  FIG. 1 . In an example of  FIG. 3  also, all the memories,  20   a  to  20   d , are 32-bit bus width DDR SDRAMs. 
     While the semiconductor device SD according to the first comparative example of  FIG. 2  includes the four semiconductor chips, SC 11  to SC 14 , the semiconductor device SD according to the second comparative example includes two semiconductor chips, SC 21  and SC 22 . The two monitors,  10   a  and  10   b , and the two memories,  20   a  and  20   b , are coupled to the semiconductor chip SC 21 . The two monitors,  10   c  and  10   d , and the two memories,  20   c  and  20   d , are coupled to the semiconductor chip SC 22 . Since the two semiconductor chips, SC 21  and SC 22 , have similar configurations, only the semiconductor chip SC 21  will be described. 
     As shown in  FIG. 3 , the semiconductor chip SC 21  includes a CPU, a graphics processing unit GPU, a display control unit DC, memory controllers MC 1  and MC 2 , memory interfaces MIF 1  and MIF 2 , and an internal bus IB. The two monitors,  10   a  and  10   b , are coupled to the display control unit DC. The memory  20   a  is coupled to the memory interface MIF 1 , and a control signal ctr 1  and a data signal dq 1  are transmitted or received between both. The memory  20   b  is coupled to the memory interface MIF 2 , and a control signal ctr 2  and a data signal dq 2  are transmitted or received between both. 
     Since the semiconductor chip SC 11  shown in  FIG. 2  includes only the single set of memory controller MC and memory interface MIF, only the single memory,  20   a , is coupled to the semiconductor chip SC 11 . Further, only the single monitor,  10   a , is coupled to the semiconductor chip SC 11 . On the other hand, the semiconductor chip SC 21  shown in  FIG. 3  includes the two sets of memory controller, MC 1  and MC 2 , and memory interface, MIF 2  and MIF 2 . Accordingly, the two memories,  20   a  and  20   b , are coupled to the semiconductor chip SC 21 . Further, the two monitors,  10   a  and  10   b , are coupled to the semiconductor chip SC 21 . The other configuration is similar to that of the semiconductor chip SC 11  according to the first comparative example and therefore will not be described. 
     As seen above, the semiconductor device SD according to the second comparative example, which includes the two semiconductor chips, SC 21  and SC 22 , can reduce the implementation area compared to the semiconductor device SD according to the first comparative example, which includes the four semiconductor chips, SC 11  to SC 14 . 
     Configuration of Semiconductor Device According to Third Comparative Example 
     Next, referring to  FIG. 4 , there will be described a semiconductor device SD according to a third comparative example examined by the inventors.  FIG. 4  is a block diagram showing an example configuration of the semiconductor device SD according to the third comparative example. As with  FIGS. 2 and 3 ,  FIG. 4  shows the internal configuration of the semiconductor device SD according to the third comparative example, as well as four monitors,  10   a  to  10   d , and four memories,  20   a  to  20   d . The four monitors,  10   a  to  10   d , correspond to the monitor  10  of  FIG. 1 , and the four memories,  20   a  to  20   d , correspond to the memory  20  of  FIG. 1 . In an example of  FIG. 3  also, all the memories,  20   a  to  20   d , are 32-bit bus width DDR SDRAMs. 
     As shown in  FIG. 4 , the semiconductor device SD according to the third comparative example includes two semiconductor chips, SC 31  and SC 32 , as with the semiconductor device SD according to the second comparative example. The two monitors,  10   a  and  10   b , and the two memories,  20   a  and  20   b , are coupled to the semiconductor chip SC 31 . On the other hand, the two monitors,  10   c  and  10   d , and the two memories,  20   c  and  20   d , are coupled to the semiconductor chip SC 32 . Since the two semiconductor chips, SC 31  and SC 32 , have similar configurations, only the semiconductor chip SC 31  will be described. 
     As shown in  FIG. 4 , the semiconductor chip SC 31  includes a CPU, a graphics processing unit GPU, a display control unit DC, memory controllers MC 1  and MC 2 , memory interfaces MIF 1  and MIF 2 , an internal bus IB, and an inter-chip interface ICIF. That is, the semiconductor chip SC 31  includes the inter-chip interface ICIF as well as the configuration of the semiconductor chip SC 21  shown in  FIG. 3 . 
     The inter-chip interface ICIF is coupled to the internal bus IB. The inter-chip interface ICIF of the semiconductor chip SC 31  is coupled to the inter-chip interface ICIF of the semiconductor chip SC 32  through a 30-bit bus. Accordingly, the CPU of the semiconductor chip SC 31  also can control the monitors  10   c  and  10   d  and the two memories,  20   c  and  20   d , coupled to the semiconductor chip SC 32 . Of course, the CPU of the semiconductor chip SC 32  also can control the monitors  10   a  and  10   b  and the two memories,  20   a  and  20   b , coupled to the semiconductor chip SC 31 . 
     As seen above, in the semiconductor device SD according to the third comparative example, the semiconductor chips SC 31  and SC 32  are coupled together through the inter-chip interfaces ICIF included therein. Accordingly, either semiconductor chip can control the four monitors,  10   a  to  10   d , and the four memories,  20   a  to  20   d . Thus, the control is facilitated. On the other hand, it is necessary to add terminals T solely for inter-chip communication, which would result in an increase in the number of terminals. In an example of  FIG. 4 , 30 terminals T must be added. 
     The inventors have contemplated of controlling an increase in the number of terminals of a semiconductor device which includes inter-chip interfaces and where multiple semiconductor chips can be coupled together. Details of the contemplation will be described below. 
     Configuration of Semiconductor Device According to First Embodiment 
     Next, referring to  FIG. 5 , a semiconductor device SD according to a first embodiment will be described.  FIG. 5  is a block diagram showing an example configuration of the semiconductor device SD according to the first embodiment.  FIG. 5  shows the internal configuration of the semiconductor device SD according to the first embodiment, as well as four monitors,  10   a  to  10   d , and four memories,  20   a  to  20   d . The four monitors,  10   a  to  10   d , correspond to the monitor  10  of  FIG. 1 , and the four memories,  20   a  to  20   d , correspond to the memory  20  of  FIG. 1 . In an example of  FIG. 5 , all the memories,  20   a  to  20   d , are 32-bit bus width DDR SDRAMs. Note that the specific values of the bus width and the like are illustrative only and can be changed as appropriate, as a matter of course. 
     As shown in  FIG. 5 , the semiconductor device SD according to the first embodiment includes two semiconductor chips, SC 1  and SC 2 . Coupled to the semiconductor chip SC 1  are two monitors,  10   a  and  10   b , and two memories,  20   a  and  20   b . Coupled to the semiconductor chip SC 2  are two monitors,  10   c  and  10   d , and two memories,  20   c  and  20   d . The semiconductor chips SC 1  and SC 2  are coupled together through inter-chip interfaces included therein. Accordingly, either semiconductor chip can control the four monitors,  10   a  to  10   d , and the four memories,  20   a  to  20   d . Since the two semiconductor chips, SC 1  and SC 2 , have similar configurations, only the semiconductor chip SC 1  will be described. 
     As shown in  FIG. 5 , the semiconductor chip SC 1  includes a CPU, a graphics processing unit GPU, a display control unit DC, memory controllers MC 1  and MC 2 , memory interfaces MIF 1  and MIF 2 , an internal bus IB, an inter-chip interface ICIF, selectors SEL 1  and SEL 2 , mode terminals MT, and a decoder DEC. The CPU, the graphics processing unit GPU, the display control unit DC, the memory controller MC, and the inter-chip interface ICIF are coupled together through the internal bus IB. Coupled to the display control unit DC are the two monitors,  10   a  and  10   b . Coupled to the memory interfaces MIF 1  and MIF 2  are the memories  20   a  and memory  20   b , respectively. 
     The CPU performs various processes in the semiconductor chip SC 1  on the basis of a control program. The control program is stored in, for example, the memory  20   a  or memory  20   b . The CPU accesses the memory  20   a  through the memory controller MC 1  and the memory interface MIF 1 . Specifically, the CPU requests the memory controller MC 1  to access the memory  20   a . Similarly, the CPU accesses the memory  20   b  through the memory controller MC 2  and the memory interface MIF 2 . 
     The CPU also can access the memory  20   c  through the inter-chip interface ICIF, as well as the inter-chip interface ICIF, the memory controller MC 1 , and the memory interface MIF 1  of the semiconductor chip SC 2 . Similarly, the CPU also can access the memory  20   d  through the inter-chip interface ICIF, as well as the inter-chip interface ICIF, the memory controller MC 2 , and the memory interface MIF 2  of the semiconductor chip SC 2 . 
     The CPU requests the display control unit DC to, for example, start displaying images or change the displayed image on the monitor  10   a  or monitor  10   b . Through the inter-chip interface ICIF, as well as the inter-chip interface ICIF of the semiconductor chip SC 2 , the CPU also can request the display control unit DC of the semiconductor chip SC 2  to, for example, start displaying images on the monitor  10   c  or monitor  10   d  or change the displayed image to another. 
     The CPU also requests the graphics processing unit GPU to render graphics. 
     The graphics processing unit GPU is an operation circuit specialized in graphics rendering. In accordance with a request from the CPU, the graphics processing unit GPU renders graphics, for example, using a program or data stored in the memory  20   a  or memory  20   b . The graphics rendered by the graphics processing unit GPU are displayed on the monitor  10   a  through the display control unit DC. 
     In accordance with a request from the CPU or graphics processing unit GPU, the memory controller MC 1  transmits 32-bit data signals dq 0  to dq 31  and a control signal ctr 1  to the memory interface MIF 1 . The memory controller MC 1  also transmits 32-bit data signals dq 0  to dq 31  received from the memory interface MIF 1  to the CPU or graphics processing unit GPU. 
     The control signal ctr 1  transmitted by the memory controller MC 1  according to the first embodiment is also received by the memory interface MIF 2  through the selector SEL 2 . That is, the memory controller MC 1  according to the first embodiment controls both the memories  20   a  and  20   b  through the memory interfaces MIF 1  and MIF 2 . 
     In an example of  FIG. 5 , both the memories  20   a  and  20   b , coupled to the memory controller MC 1  through the memory interfaces MIF 1  and MIF 2 , are 32-bit bus width DDR SDRAMs. Accordingly, the memory controller MC 1  is composed of a DDR SDRAM bus state controller (DBSC) for a 64-bit bus width DDR SDRAM. 
     In accordance with a request from the CPU or graphics processing unit GPU, the memory controller MC 2  transmits 32-bit data signals dq 32  to dq 63  to the memory interface MIF 2 . The memory controller MC 2  also transmits data signals dq 32  to dq 63  received from the memory interface MIF 2  to the CPU or graphics processing unit GPU. In this case, a control signal line between the memory controller MC 2  and the memory interface MIF 2  is previously split by the selector SEL 2 . Thus, the memory controller MC 2  only transfers the data signals dq 32  to dq 63 . 
     As will be described in detail later, by changing the setting of the mode terminals MT to switch the selectors SEL 1  and SEL 2 , it is possible to change the operation mode of the semiconductor chip SC 1 . In the operation mode in which inter-chip communication is used (hereafter referred to as the inter-chip communication mode) shown in  FIG. 5 , the memory controller MC 1  controls both the memories  20   a  and  20   b  and therefore the memory controller MC 2  does not control the memory  20   b.    
     Alternatively, an operation mode in which the semiconductor chip SC 1  is used singly (hereafter referred to as the single mode) may be used.  FIG. 6  is a block diagram of the semiconductor chip SC 1  according to the first embodiment which is placed in the single mode. The selections made by the selectors SEL 1  and SEL 2  in  FIG. 6  differ from the selections made thereby in  FIG. 5 . Specifically, as in  FIG. 5 , the control signal ctr 1  output from the memory controller MC 1  is input to the memory  20   a  through the memory interface MIF 1 . On the other hand, unlike in  FIG. 5 , a control signal ctr 2  output from the memory controller MC 2  is input to the memory  20   b  through the memory interface MIF 2 . That is, the memory controller MC 1  controls the memory  20   a , and the memory controller MC 2  controls the memory  20   b.    
     As seen above, in the single mode shown in  FIG. 6 , the memory controller MC 2  controls the memory  20   b , which is a 32-bit bus width DDR SDRAM. Accordingly, the memory controller MC 2  is composed of a DDR SDRAM bus state controller (DBSC) for a 32-bit bus width DDR SDRAM. 
     Referring back to  FIG. 5 , the memory interface MIF 1  sequentially outputs the control signal ctr 1  and 32-bit data signals dq 0  to dq 31  received from the memory controller MC 1  to the memory  20   a . The memory interface MIF 1  also transmits 32-bit data signals dq 0  to dq 31  received from the memory  20   a  to the memory controller MC. In the example of  FIG. 5 , the memory  20   a  and the memory interface MIF 1  are coupled together through a 32-bit data signal bus and a 30-bit control signal bus. 
     The memory interface MIF 2  sequentially outputs the 32-bit data signals dq 32  to dq 63  received from the memory controller MC 2  to the memory  20   b . The memory interface MIF 2  also transmits 32-bit data signals dq 32  to dq 63  received from the memory  20   b  to the memory controller MC 2 . In the example of  FIG. 5 , the memory  20   b  and the memory interface MIF 2  are coupled together through a 32-bit data signal bus. 
     Referring now to  FIG. 7 , the internal configuration of the memory interface MIF 1  will be described.  FIG. 7  is a circuit diagram showing the internal configuration of the memory interface MIF 1 . As shown in  FIG. 7 , the memory interface MIF 1  includes a control signal input/output circuit and a data signal input/output circuit. 
     The control signal input/output circuit includes 28 sets of input buffer IBF and output buffer OBF and also includes one differential buffer. Each output buffer OBF amplifies the control signal ctr 1  received from the memory controller MC 1  and outputs the amplified signal to the memory  20   a . Each input buffer IBF amplifies the control signal ctr 1  received from the memory  20   a  and outputs the amplified signal to the memory controller MC 1 . The differential buffer differentially amplifies a clock signal received from the memory controller MC 1  and outputs a clock signal clk and an inverted clock signal clkb. 
     As shown in  FIG. 7 , the 30-bit control signal ctr 1  includes the clock signal clk and the inverted clock signal clkb, as well as address signals a 0 , a 1 , a 2 , and the like, bank address signals ba 0 , ba 1 , ba 2 , and the like, a row address strobe (RAS) signal ras, a column address strobe (CAS) signal cas, a write enable signal we, a chip select signal cs, an on die termination (ODT) signal odt, and the like. 
     On the other hand, the data signal input/output circuit includes 32 sets of input buffer IBF and output buffer OBF. Each output buffer OBF amplifies one of the data signals dq 0  to dq 31  received from the memory controller MC 1  and outputs the amplified signal to the memory  20   a . Each input buffer IBF amplifies one of the data signals dq 0  to dq 31  received from the memory  20   a  and outputs the amplified signal to the memory controller MC 1 . 
     Referring back to  FIG. 5 , description will be continued. 
     The inter-chip interface ICIF is coupled to the internal bus IB. The inter-chip interface ICIF of the semiconductor chip SC 1  is coupled to the inter-chip interface ICIF of the semiconductor chip SC 2  through the selector SEL 1 , the control terminal CT, and a 30-bit bus. Thus, the CPU of the semiconductor chip SC 1  also can control the monitors  10   c  and  10   d  and the two memories,  20   c  and  20   d , coupled to the semiconductor chip SC 2 . Of course, the CPU of the semiconductor chip SC 2  also can control the monitors  10   a  and  10   b  and the two memories,  20   a  and  20   b , coupled to the semiconductor chip SC 1 . 
     Referring now to  FIG. 8 , the internal configuration of the inter-chip interface ICIF will be described.  FIG. 8  is a block diagram showing the internal configuration of the inter-chip interface ICIF. As shown in  FIG. 8 , the inter-chip interface ICIF of the semiconductor chip SC 1  includes input/output control units IOC 1  and IOC 2  and signal conversion units SCU 1  and SCU 2 . Since the input/output control units IOC 1  and IOC 2  have similar configurations, only the input/output control unit IOC 1  will be described. Since the signal conversion units SCU 1  and SCU 2  also have similar configurations, only the signal conversion unit SCU 1  will be described. 
     As shown in  FIG. 8 , the input/output control unit IOC 1  includes two output buffers, OBF 1  and OBF 2 , two input buffers, IBF 1  and IBF 2 , two FIFO circuits, FIFO 1  and FIFO 2 , and an arbiter ARB. The signal conversion unit SCU 1  includes a selector SEL 3 , a decoder DEC 1 , an encoder ENC 1 , a serial/parallel conversion unit SPC, and a parallel/serial conversion unit PSC. 
     Hereafter, description will be made along the flow of signals. 
     A 64-bit request req 1  from a transmission port is input to the arbiter ARB through the input buffer IBF 1  and the FIFO circuit FIFO 1 . On the other hand, a 64-bit response res 2  from a reception port is input to the arbiter ARB through the input buffer IBF 2  and the FIFO circuit FIFO 2 . When the request req 1  from the transmission port and the response res 2  from the reception port compete with each other, the arbiter ARB selects one of these signals and outputs the selected signal to the encoder ENC 1 . 
     The 64-bit request req 1  or 64-bit response res 2  input to the encoder ENC 1  is compressed into an 8-bit signal and encoded by the encoder ENC 1 . The 8-bit request reg 1  or 8-bit response res 2 , which is a parallel signal, is converted into a serial signal and output to the semiconductor chip SC 2  by the parallel/serial conversion unit PSC. The 8-bit request reg 1  or 8-bit response res 2  input to the semiconductor chip SC 2  is decompressed into a 64-bit signal and decoded. Subsequently, the 64-bit request reg 1  is received through a reception port; the 64-bit response res 2  is received through a transmission port. 
     On the other hand, a 64-bit request req 2  transmitted through the transmission port of the semiconductor chip SC 2  or a 64-bit res 1  transmitted via the reception port of the semiconductor chip SC 2  is compressed into an 8-bit signal and encoded by the inter-chip interface ICIF of the semiconductor chip SC 2 . The 8-bit request req 2  or 8-bit response res 1 , which is a serial signal, is input to the serial/parallel conversion unit SPC of the semiconductor chip SC 1  and converted into a parallel signal. 
     The 8-bit request req 2  or 8-bit response res 1  output from the serial/parallel conversion unit SPC is decompressed into a 64-bit signal and decoded by the decoder DEC 1 . The 64-bit request req 2  or 64-bit response res 1  is input to the selector SEL 3 . Based on a control signal s 1 , the selector SEL 3  outputs the 64-bit request req 2  to the FIFO circuit FIFO 2  or outputs the 64-bit response res 1  to the FIFO circuit FIFO 1 . Subsequently, the 64-bit request req 2  is input to the reception port through the output buffer OBF 2 ; the 64-bit response res 1  is input to the transmission port through the output buffer OBF 1 . 
     As seen above, the transmission signals are compressed by the inter-chip interfaces ICIF of the semiconductor chips SC 1  and SC 2 . Thus, the number of inter-chip communication terminals can be reduced. In an example of  FIG. 10 , the signal conversion unit SCU 1  transmits or receives an 8-bit signal obtained by compressing a 64-bit signal, a clock signal clk (1 bit), and an inverted clock signal clkb (1 bit). That is, the signal conversion unit SCU 1  transmits or receives the signals of 10 bits and therefore has 20 terminals. The signal conversion unit SCU 2  transmits or receives a 4-bit signal obtained by converting a 16-bit signal, and a clock signal clk (1 bit). That is, the signal conversion unit SCU 2  transmits or receives the signals of 5 bits and therefore has 10 terminals. Accordingly, the inter-chip interface ICIF of the semiconductor chip SC 1  has a total of 30 inter-chip communication terminals. 
     The semiconductor device SD according to the first embodiment uses 30 control terminals CT for outputting control signals from the memory interface MIF 2 , as inter-chip interface terminals. As described above, the transmission signals are compressed by the inter-chip interfaces ICIF. Thus, it is possible to reduce the number of terminals necessary for inter-chip communication to the number of control terminals CT or less. 
     Referring back to  FIG. 5 , description will be continued. 
     Based on an operation mode signal mod from the decoder DEC, the selector (first selector) SEL 1  changes the signal line coupled to the control terminal CT to another. Specifically, the selector SEL 1  selects between a control signal line coupled to the memory interface MIF 2  and a signal line coupled to the inter-chip interface ICIF and couples the selected signal line to the control terminal CT. In the operation mode of  FIG. 5 , the inter-chip interface ICIF is coupled to the control terminal CT. 
     Based on an operation mode signal mod from the decoder DEC, the selector (second selector) SEL 2  changes the control signal line coupled to the memory interface MIF 2  to another. Specifically, the selector SEL 2  selects between a control signal line coupled to the memory controller MC 1  and a control signal line coupled to the memory controller MC 2  and couples the selected signal line to the memory interface MIF 2 . In other words, the selector SEL 2  selects between a control signal ctr 1  from the memory controller MC 1  and a control signal ctr 2  from the memory controller MC 2  and inputs the selected control signal to the memory interface MIF 2 . In the inter-chip communication mode shown in  FIG. 5 , the control signal ctr 1  from the memory controller MC 1  is input to the memory interface MIF 2 . 
     The mode terminals MT are terminals for setting the operation mode. For example, in accordance with a set value corresponding to the operation mode, a value 1 (H: high) or value 0 (L: low) is assigned to each mode terminal MT. While the number of the mode terminals MT is two in the example of  FIG. 5 , the number of mode terminals MT is changed according to the number of operation modes as appropriate. For example, if the number of operation modes is two, a single mode terminal MT is sufficient. For example, if the number of operation modes is 4 or less, two mode terminals MT are sufficient. Generally, if the number of operation modes is 2 n  or less, n (n is a natural number) number of mode terminals MT are sufficient. Note that the operation mode is determined in the design stage in principle and therefore cannot be changed after the semiconductor device SD is implemented. That is, the operation mode is not changed during operation of the semiconductor device SD. 
     The decoder DEC decodes the set value of the mode terminals MT to generate an operation mode signal mod. If the number of mode terminals MT is one (the number of operation modes is two), the decoder DEC is not needed. 
     Next, referring to  FIG. 9 , there will be described an example of disposition of the terminals T (including the control terminals CT and the mode terminals MT) of the semiconductor chip SC 1 .  FIG. 9  is a plan view showing an example of disposition of the terminals T of the semiconductor chip SC 1 . The terminals T include the control terminals CT and the mode terminals MT. In  FIG. 9 , the back surface of the semiconductor chip SC 1  having the terminals T disposed thereon forms an x-y plane. The values described below the semiconductor chip SC 1  represent x coordinates, and the values described on the left of the semiconductor chip SC 1  represent y coordinates. In an example of  FIG. 9 , 25 terminals T are disposed in the x-axis direction, and 25 terminals T are disposed in the y-axis direction. However, no terminals T are disposed in the area of X=6 to 9 and 17 to 20 and Y=6 to 9 and 17 to 20. That is, 25×25−15×15+7×7=449 terminals T are disposed. Of course, these specific values are illustrative only. 
     Next, referring to  FIG. 10 , assignment of signals to terminals disposed in a broken line frame (x=1 to 5 and y=1 to 5) of  FIG. 9  will be described.  FIG. 10  is a diagram showing assignment of signals to the terminals disposed in the broken line frame (x=1 to 5 and y=1 to 5) of  FIG. 9 . A total of 25 squares of x=1 to 5 and y=1 to 5 in  FIG. 10  correspond to 25 terminals disposed in the broken line frame of  FIG. 9  (x=1 to 5 and y=1 to 5).  FIG. 10  shows that a high-potential power supply voltage signal is assigned to VDD; a low-potential power supply voltage signal to VSS; a control signal ctr 2  from the memory interface MIF 2  to CNT; and a data signal dq from the memory interface MIF 2  to DQ. 
     A terminal represented by CNT in  FIG. 10  is the control terminal CT coupled to the inter-chip interface ICIF through the selector SEL 1  in  FIG. 5 . As shown in  FIG. 10 , at least one of a terminal for a high-potential power supply signal VDD and a terminal for a low-potential power supply signal VSS is disposed adjacent to the control terminal CT for DDR SDRAM. 
     Thus, the impedance of the line coupled to the control terminal CT is reduced, so that crosstalk is suppressed during memory access. As seen above, the semiconductor device SD according to the first embodiment uses the control terminal CT for DDR SDRAM as an inter-chip communication terminal. Thus, excellent inter-chip communication characteristics can be achieved. 
     Effects of Semiconductor Device According to First Embodiment 
     As seen above, in the semiconductor device SD according to the first embodiment, the semiconductor chips SC 1  and SC 2  are coupled together through the inter-chip interfaces ICIF included therein. Thus, either semiconductor chip can control the four monitors,  10   a  to  10   d , and the four memories,  20   a  to  20   d . As a result, the control is facilitated. 
     Further, the semiconductor device SD according to the first embodiment includes the selectors SEL 1  and SEL 2 , which can do switching in accordance with the operation mode set by the mode terminals MT. The semiconductor device SD according to the first embodiment uses the control terminal CT, which outputs a control signal transmitted from the memory interface MIF 2  in the single mode, as an inter-chip communication terminal in the inter-chip communication mode. Thus, the number of terminals is smaller than that in the third comparative example ( 30  in the example of  FIG. 4 ). That is, the semiconductor device SD according to the first embodiment can perform inter-chip communication, as well as controls an increase in the number of terminals. Note that while the semiconductor device SD according to the first embodiment needs to additionally include mode terminals MT, it only has to include at most two or three mode terminals MT as described above. 
     Second Embodiment 
     Configuration of Semiconductor Device According to Second Embodiment 
     Next, referring to  FIG. 11 , a semiconductor device SD according to a second embodiment will be described.  FIG. 11  is a block diagram showing an example configuration of the semiconductor device SD according to the second embodiment.  FIG. 11  shows the internal configuration of the semiconductor device SD according to the second embodiment, as well as four memories,  20   a  to  20   d . In an example of  FIG. 11 , all the memories,  20   a  to  20   d , are 32-bit bus width DRAMs. Of course, the specific values of the bus width and the like are illustrative only and can be changed as appropriate. 
     As shown in  FIG. 11 , the semiconductor device SD according to the second embodiment includes two semiconductor chips, SC 1  and SC 2 . Coupled to the semiconductor chip SC 1  are the two monitors,  20   a  and  20   b . Coupled to the semiconductor chip SC 2  are the two memories,  20   c  and  20   d . The semiconductor chips SC 1  and SC 2  are coupled together through inter-chip interfaces included therein. Thus, either semiconductor chip can control the four memories,  20   a  to  20   b . Since the two semiconductor chips, SC 1  and SC 2 , have similar configurations, only the semiconductor chip SC 1  will be described. 
     As shown in  FIG. 11 , the semiconductor device SD according to the second embodiment does not include the graphics processing unit GPU or display control unit DC included in the semiconductor device SD shown in  FIG. 5 , nor is it coupled to any monitor. As seen above, the semiconductor device SD according to the second embodiment is not intended to control display of images. Rather it can be used for other purposes. For example, the semiconductor device SD according to the second embodiment can be used in electronic devices other than car navigation systems, such as mobile phones, portable game machines, tablet personal computers (PCs), and notebook PCs. 
     Since the semiconductor device SD according to the second embodiment has only two operation modes, the inter-chip communication mode and the single mode, it has only one mode terminal MT. Accordingly, the semiconductor device SD according to the second embodiment does not include the decoder DEC included in the semiconductor device SD shown in  FIG. 5 . The other configuration is similar to that of the semiconductor device SD according to the first embodiment shown in  FIG. 5  and therefore will not be described. 
       FIG. 12  is a block diagram of the semiconductor chip SC 1  according to the second embodiment which is placed in the single mode. The selections made by the selectors SEL 1  and SEL 2  in  FIG. 12  differ from the selections made thereby in  FIG. 11 . Specifically, as in  FIG. 11 , a control signal ctr 1  from the memory controller MC 1  is input to the memory  20   a  through the memory interface MIF 1 . On the other hand, unlike in  FIG. 11 , a control signal ctr 2  from the memory controller MC 2  is input to the memory  20   b  through the memory interface MIF 2 . That is, the memory controller MC 1  controls the memory  20   a , and the memory controller MC 2  controls the memory  20   b.    
     Effects of Semiconductor Device According to Second Embodiment 
     As seen above, in the semiconductor device SD according to the second embodiment, the semiconductor chips SC 1  and SC 2  are coupled together through the inter-chip interfaces ICIF included therein. Thus, either semiconductor chip can control the four memories,  20   a  to  20   b . Thus, the control is facilitated. 
     Further, the semiconductor device SD according to the second embodiment includes the selectors SEL 1  and SEL 2 , which can do switching in accordance with the operation mode set by the mode terminal MT. The semiconductor device SD according to the second embodiment uses the control terminal CT, which outputs a control signal transmitted from the memory interface MIF 2  in the single mode, as an inter-chip communication terminal in the inter-chip communication mode. Thus, the number of terminals is smaller than that in the third comparative example ( 30  in the example of  FIG. 4 ). That is, as with the semiconductor device SD according to the first embodiment, the semiconductor device SD according to the second embodiment can perform inter-chip communication, as well as controls an increase in the number of terminals. Specifically, compared to the third comparative example shown in  FIG. 4 , the semiconductor device SD according to the second embodiment shown in  FIG. 11  additionally includes one mode terminal MT but reduces 30 inter-chip communication terminals. As a result, 29 terminals can be reduced. 
     While the present invention has been described in detail based on the embodiments, the invention is not limited thereto. As a matter of course, various changes can be made to the embodiments without departing from the spirit and scope of the invention.