Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor integrated circuit having a plurality of output modes with variable bus widths. 
     2. Description of the Related Art 
     There was a semiconductor integrated circuit in which the output bit width can be changed in accordance with a device connected to the outside of the semiconductor integrated circuit. For example, in a semiconductor integrated circuit having a 16-bit bus mode and an 8-bit bus mode, sixteen outgoing I/O portions are provided so that the sixteen outgoing I/O portions output respective bits of 16-bit data in the 16-bit bus mode whereas eight I/O portions corresponding to less significant 8 bits are selected from the sixteen outgoing I/O portions in the 8-bit bus mode and used for outputting data while the output for more significant 8 bits is fixed or the input for more significant 8 bits is pulled down or up. 
       FIG. 7  is a diagram showing the configuration of I/O portions of a semiconductor integrated circuit according to the background art. The semiconductor integrated circuit according to the background art includes a set of AND circuits  701 , a set of output buffers  702 , and a set of outgoing I/O portions  703  (16 bits of IO 0  to IO 15 ). These constituent members  701  to  703  are separated into a group corresponding to more significant bits (IO 8  to IO 15 ) and a group corresponding to less significant bits (IO 0  to IO 7 ). 
     OUT 0  to OUT 15  are output signals generated by the internal operation of the semiconductor integrated circuit and outputted to the outside. MODE 16 B is an output mode switching signal. When MODE 16 B is high (H) in level, a 16-bit bus mode is selected. When MODE 16 B is low (L) in level, an 8-bit bus mode is selected. Specifically, when MODE 16 B is L, the output of the set of AND circuits is fixed to L to thereby select an 8-bit bus mode. 
     OE 8 H is an output control signal for controlling the set of output buffers  702  for the more significant bits. When OE 8 H is H, IO 8  to IO 15  are outputted normally. When OE 8 H is L, a half of the set of output buffers  702  corresponding to IO 8  to IO 15  become a high impedance state (HiZ). OE 8 L is an output control signal controlling the set of output buffers  702  for the less significant bits. When OE 8 L is H, IO 0  to IO 7  are outputted normally. When OE 8 L is L, a half of the set of output buffers  702  corresponding to IO 0  to IO 7  become HiZ. 
     In the 16-bit bus mode where MODE 16 B is H, OUT 0  to OUT 15  are outputted to IO 0  to IO 15  directly if OE 8 H is H and OE 8 L is H. In the 8-bit bus mode where MODE 16 B is L, the output for IO 8  to IO 15  is fixed to L if OE 8 H is H, but IO 8  to IO 15  are pulled down or up to pull-down or pull-up resistors if OE 8 H is L. When OE 8 L is H, OUT 0  to OUT 7  are outputted to IO 0  to IO 7  directly. 
     In this configuration, the quantity of data allowed to be outputted at once in the 8-bit output mode is a half of the quantity of data in the 16-bit output mode. For this reason, an output speed twice as high as the output speed in the 16-bit output mode is required in the 8-bit output mode for obtaining the same transfer rate as that in the 16-bit output mode. When such a high-speed operation is performed, increase in output current capacity is required. 
     As a technique for changing external output current capacity of a semiconductor integrated circuit, there has been heretofore proposed a semiconductor device having such a circuit configuration that transistor drive capacity can be changed on the basis of an external signal in order to improve the margin for test reading (e.g. see Japanese Patent Laid-Open No. 79056/1991). 
     As described above, if a constant transfer rate is required in data outputting in a semiconductor integrated circuit having a plurality of output modes with variable bus widths such as a 16-bit output mode and an 8-bit output mode, an output speed twice as high as that in the 16-bit output mode is required in the 8-bit output mode. There is a possibility that no mode but the 8-bit mode can be used for the structural reason of the external device. When such a high-speed operation is performed, the semiconductor integrated circuit cannot be operated normally if output current capacity is low. 
     The background-art technique for changing transistor drive capacity in the external output of the semiconductor integrated circuit is a technique by which transistor drive capacity can be lowered in order to improve the margin for test reading. The idea of changing external output current capacity in accordance with necessity is effective. This technique however has a disadvantage in that the external output circuit becomes complex because the transistor drive capacity is changed. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a semiconductor integrated circuit provided with a plurality of output modes with variable bus widths, in which output current drive capacity can be improved without use of any special external output circuit in an output mode with a small bus width, so that a high-speed operation can be performed to obtain the same data transfer rate as in an output mode with a large bus width. 
     The invention provides a semiconductor integrated circuit provided with a plurality of output modes including an (m×n)-bit (in which m is a natural number not smaller than 2 and n is a natural number) output mode and an n-bit output mode different in bus width, wherein: the semiconductor integrated circuit includes (m×n) I/O portions for outputting signals to the outside; in the (m×n)-bit output mode, the (m×n) I/O portions output data with a bus width of (m×n) bits; and in the n-bit output mode, the (m×n) I/O portions output data with a bus width of n bits so that the data are multiplexed in at least two I/O portions per bit. 
     According to the aforementioned configuration, (m−1)×n outgoing I/O portions which have been heretofore not used in the n-bit output mode can be used so that data can be outputted from at least two outgoing I/O portions per bit. Accordingly, output current drive capacity of at least two I/O portions per bit can be obtained in an external device by a method of short-circuiting the outgoing I/O portions which output one and the same data. As a result, current drive capacity twice or higher per bit can be obtained, so that the value of output delay can be reduced to make a high-speed operation possible. 
     In the invention, the semiconductor integrated circuit further includes first selectors for selecting signals to be transferred to the I/O portions respectively; and each of the first selectors selects one bit from data with the bus width of (m×n) bits in the (m×n)-bit output mode whereas each of the first selectors selects one bit from data with the bus width of n bits in the n-bit output mode. 
     Further, in the invention, the first selectors include (n−1) sets of m selectors, and a set of (m−1) selectors; and the selectors select different bits respectively from data with the bus width of (m×n) bits in the (m×n)-bit output mode whereas each set of selectors select one and the same bit from data with the bus width of n bits in the n-bit output mode. 
     According to the aforementioned configuration, data with a bus width of (m×n) bits can be outputted in the (m×n)-bit output mode whereas data with a bus width of n bits can be outputted multiply in accordance with each bit in the n-bit output mode. Accordingly, a circuit for giving current drive capacity twice or higher per bit in the n-bit output mode can be achieved easily. 
     Further, in the invention, the semiconductor integrated circuit further includes (m×n) tristate buffers for driving the (m×n) I/o portions respectively; and in the n-bit output mode, (k×n) tristate buffers (in which k is a natural number not smaller than 1 but smaller than m) among the (m×n) tristate buffers become high in impedance. 
     According to the aforementioned configuration, the tristate buffers are controlled so that the output mode of data with a bus width of n bits in the n-bit output mode can be selected as to whether the data are outputted multiply in accordance with bits or whether the data are outputted by use of one I/O portion per bit in accordance with condition. Accordingly, the trade-off relation between high speed and low noise can be selected in accordance with current drive capacity. 
     Further, in the invention, the (m×n) I/O portions are bidirectional I/O portions provided with (m×n) input buffers respectively. 
     Further, in the invention, the semiconductor integrated circuit further includes first selectors for selecting signals to be transferred to the I/O portions respectively, and second selectors for selecting signals to be inputted to the first selectors respectively; each of the first selectors selects one bit from data with the bus width of (m×n) bits in the (m×n)-bit output mode whereas the first selectors select bits corresponding to signals outputted from the second selectors in the n-bit output mode; and in the n-bit output mode, each of the second selectors selects one bit from data with the bus width of n bits or selects a signal different from the data with the bus width of (m×n) bits and different from the data with the bus width of n bits. 
     According to the aforementioned configuration, when one I/O portion per bit is selected in the n-bit output mode, the other I/O portion on the unused side can be used for outputting a signal such as a test signal or an ICE signal different from the ordinary output signal selected by each second selector. 
     Further, in the invention, in the case where m is equal to 2, a 2n-bit output mode and an n-bit output mode are provided; in the 2n-bit output mode, the s-th one (1≦s≦2n) of the 2n I/O portions outputting data with a bus width of 2n bits outputs the s-th bit of data with the bus width of 2n bits; and in the n-bit output mode, the (2t−1)-th and 2t-th ones (1≦t≦n) of the 2n I/O portions output the t-th bit of data with the bus width of n bits. 
     According to the aforementioned configuration, data with a bus width of 2n bits can be outputted in order in the 2n-bit output mode while data with a bus width of n bits can be outputted in order to adjacent two I/O portions per bit in the n-bit output mode. Accordingly, in the n-bit output mode, current drive capacity twice per bit can be obtained easily when adjacent two I/O portions are short-circuited. 
     Further, in the invention, the semiconductor integrated circuit further includes (2n−1) selectors provided so as to correspond to the second to 2n-th ones of the 2n I/O portions; in the 2n-bit output mode, the s-th selector selects the s-th bit of data with the bus width of 2n bits; and in the n-bit output mode, the (2t−1)-th and 2t-th selectors select the t-th bit of data with the bus width of n bits. 
     According to the aforementioned configuration, it is easy to achieve a circuit which can output data with a bus width of 2n bits in order in the 2n-bit output mode, and which can output data with a bus width of n bits in order to adjacent two I/O portions per bit in the n-bit output mode. 
     Further, in the invention, ascending order of the (m×n) I/O portions can be switched over to descending order by setting, and vice versa. 
     According to the aforementioned configuration, a function useful for a specific purpose can be provided because ascending order of data outputted from the (m×n) I/O portions can be switched over to descending order, and vice versa. 
     According to the invention, in a semiconductor integrated circuit having a plurality of output modes with variable bus widths, current drive capacity can be improved without use of any special external output circuit in an output mode with a small bus width. Accordingly, the value of output delay becomes so small that a high-speed operation can be performed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing the configuration of I/O portions of a semiconductor integrated circuit according to Embodiment 1 of the invention. 
         FIG. 2  is a diagram showing the configuration of I/O portions of a semiconductor integrated circuit according to Embodiment 2 of the invention. 
         FIG. 3  is a diagram showing the configuration of I/O portions of a semiconductor integrated circuit according to Embodiment 3 of the invention. 
         FIG. 4  is a diagram showing the configuration of I/O portions of a semiconductor integrated circuit according to Embodiment 4 of the invention. 
         FIG. 5  is a diagram showing the configuration of I/O portions of a semiconductor integrated circuit according to Embodiment 5 of the invention. 
         FIG. 6  is a view showing an example in which two outgoing I/O portions are short-circuited in board wiring. 
         FIG. 7  is a diagram showing the configuration of I/O portions of a semiconductor integrated circuit according to the background art. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the invention will be described below with reference to the drawings. Incidentally, in the following description, signal H expresses a signal with a high level (logical value: 1), signal L expresses a signal with a low level (logical value: 0), and HiZ expresses a high impedance state of a tristate buffer. 
     Embodiment 1 
       FIG. 1  is a diagram showing the configuration of I/O portions of a semiconductor integrated circuit according to Embodiment 1 of the invention. In  FIG. 1 , the semiconductor integrated circuit includes a set of selectors  101 , a set of output buffers (a set of tristate buffers)  102 , and a set of outgoing I/O portions  103  (IO 0  to IO 15 ). 
     OUT 0  to OUT 15  are output signals generated by the operation of an internal circuit of the semiconductor integrated circuit and outputted to the outside. MODE 16 B is an output mode switching signal. When MODE 16 B is H, a 16-bit bus mode is selected. When MODE 16 B is L, an 8-bit bus mode is selected. OE is an output control signal. When OE is H, IO 0  to IO 15  perform ordinary outputting. When OE is L, the set of output buffers  102  for IO 0  to IO 15  become HiZ. 
     In the 16-bit bus mode where MODE 16 B is H, the set of selectors  101  select wires connected on upper sides respectively. As a result, OUT 0  to OUT 15  are connected to the outgoing I/O portions IO 0  to IO 15  respectively. If OE is H. OUT 0  to OUT 15  are outputted to the outgoing I/O portions IO 0  to IO 15  directly. 
     In the 8-bit bus mode where MODE 16 B is L, the set of selectors  101  select wires connected on lower sides respectively. As a result, OUT 0  is connected to two outgoing I/O portions IO 0  and IO 1 , OUT 1  is connected to two outgoing I/O portions IO 2  and IO 3 , OUT 2  is connected to two outgoing I/O portions IO 4  and IO 5 , OUT 3  is connected to two outgoing I/O portions IO 6  and IO 7 , OUT 4  is connected to two outgoing I/O portions IO 8  and IO 9 , OUT 5  is connected to two outgoing I/O portions IO 10  and IO 11 , OUT 6  is connected to two outgoing I/O portions IO 12  and IO 13 , and OUT 7  is connected to two outgoing I/O portions IO 14  and IO 15 . 
     OUT 0  to OUT 7  are output signals in the 8-bit bus mode. When OE is turned to H, two outgoing I/O portions per bit output one and the same data. Data can be inputted into an external device by use of two outgoing I/O portions per bit in such a manner that the two outgoing I/O portions are short-circuited. 
       FIG. 6  shows an example of configuration in the case where two outgoing I/O portions are short-circuited by use of board wiring. In  FIG. 6 , the reference numeral  601  designates a semiconductor integrated circuit having I/O portions according to this embodiment;  602 , wiring on a board; and BP 0  to BP 7 , external bus ports. When wiring is performed on the board in this manner, BP 0  is connected to IO 0  and IO 1  so that current drive capacity of two outgoing I/O portions is obtained in accordance with OUT 0 . BP 1  is connected to IO 2  and IO 3  so that current drive capacity of two outgoing I/O portions is obtained in accordance with OUT 1 . The same thing can be said on BP 2  to BP 7 . 
     Embodiment 2 
     Although Embodiment 1 has been described on the case where IO 0  to IO 15  are used only as output portions, IO 0  to IO 15  can be used as bidirectional I/O portions. This embodiment shows the case where IO 0  to IO 15  are used as bidirectional I/O portions. 
       FIG. 2  is a diagram showing the configuration of I/O portions of a semiconductor integrated circuit according to Embodiment 2 of the invention. In  FIG. 2 , the semiconductor integrated circuit includes a set of selectors  101 , a set of output buffers (a set of tristate buffers)  102 , a set of bidirectional I/O portions  203  (IO 0  to IO 15 ), a set of input buffers (a set of tristate buffers)  204 , and a set of selectors  205 . 
     OUT 0  to OUT 15  are output signals generated by the internal operation of the semiconductor integrated circuit and outputted to the outside. IN 0  to IN 15  are input signals inputted from an external device into the semiconductor integrated circuit. 
     MODE 16 B is an output mode switching signal. When MODE 16 B is H, a 16-bit bus mode is selected. When MODE 16 B is L, an 8-bit bus mode is selected. OE is an output control signal. When OE is H, IO 0  to IO 15  are outputted ordinarily. When OE is L, the set of output buffers  102  for IO 0  to IO 15  become HiZ. 
     Because the operation for outputting data is the same as in Embodiment 1, the description of the operation will be omitted here. This embodiment is different from Embodiment 1 in that the set of output buffers  102  are made HiZ to thereby input data from the external device into the semiconductor integrated circuit. 
     For inputting data in the 16-bit mode, while OE is turned to L to make the set of output buffers  102  HiZ, MODE 16 B is turned to H to make the set of selectors  205  select upper wires. Accordingly, data of IO 0  is inputted into IN 0 , and data of IO 1  is inputted into IN 1 . Data of IO 2  to IO 5  are inputted into IN 2  to INS respectively in the same manner as described above. 
     For inputting data in the 8-bit mode, while OE is turned to L to make the set of output buffers  102  HiZ, MODE 16 B is turned to L. Accordingly, the set of selectors  205  select lower wires. 
     This embodiment will be described with reference to  FIG. 6  showing a state in which the semiconductor integrated circuit is mounted on the board. In the 8-bit mode, data outputted from the external device to BP 0  is inputted into IN 0  via IO 0 . Similarly, data outputted to BP 1  is inputted into IN 1  via  102 , and data outputted to BP 2  is inputted into IN 2  via  104 . As for BP 3  to BP 7 , data are inputted into IN 3  to IN 7  in the same manner as described above. Because the 8-bit mode is selected now, IN 8  to IN 15  are not used. 
     Embodiment 3 
     Although Embodiments 1 and 2 have been described on the case where two outgoing I/O portions per bit are made to perform the same operation in the 8-bit bus mode, the operation of only one outgoing I/O portion per bit may be required in accordance with the situation. This embodiment is achieved in such a manner that a function of selecting either two I/O portions or one I/O portion per bit as I/O portions operated in the 8-bit bus mode is added to Embodiment 2. 
       FIG. 3  is a diagram showing the configuration of I/O portions of a semiconductor integrated circuit according to Embodiment 3 of the invention. The semiconductor integrated circuit shown in  FIG. 3  is configured so that the set of output buffers  102  in Embodiment 2 shown in  FIG. 2  is separated into a first set of output buffers  302 E corresponding to even-number bits and a second set of output buffers  3020  corresponding to odd-number bits, and that the first set of output buffers  302 E and the second set of output buffers  3020  are controlled by different signal lines respectively. 
     OE_EVEN is an output control signal for controlling the first set of output buffers  302 E. OE_ODD is an output control signal for controlling the second set of output buffers  3020 . When OE_EVEN is H, even-number bits IO 0 , IO 2 , IO 4 , IO 6 , IO 8 , IO 10 , IO 12  and IO 14  are outputted ordinarily. When OE_EVEN is L, the first set of output buffers  302 E become HiZ. When OE_ODD is H, odd-number bits IO 1 , IO 3 , IO 5 , IO 7 , IO 9 , IO 11 , IO 13  and IO 15  are outputted ordinarily. When OE_ODD is L, the second set of output buffers  3020  become HiZ. 
     In the 16-bit bus mode where MODE 16 B is H, OUT 0  to OUT 15  are outputted to IO 0  to IO 15  directly if OE_EVEN is H and OE_ODD is H. IO 0  to IO 15  are inputted into IN 0  to IN 15  directly if OE_EVEN is L and OE_ODD is L. 
     In the 8-bit bus mode where MODE 16 B is L, OUT 0  is outputted to IO 0  and IO 1 , OUT 1  is outputted to IO 2  and IO 3 , OUT 2  is outputted to IO 4  and IO 5 , OUT 3  is outputted to IO 6  and IO 7 , OUT 4  is outputted to IO 8  and IO 9 , OUT 5  is outputted to IO 10  and IO 11 , OUT 6  is outputted to IO 12  and IO 13 , and OUT 7  is outputted to IO 14  and IO 15  if OE_EVEN is H and OE_ODD is H. 
     When two I/O portions are short-circuited by use of board wiring as shown in  FIG. 6  in the same manner as in Embodiment 1, BP 0  is connected to IO 0  and IO 1  so that current drive capacity of two outgoing I/O portions is obtained in accordance with OUT 0 . BP 1  is connected to IO 2  and IO 3  so that current drive capacity of two outgoing I/O portions is obtained in accordance with OUT 1 . The same thing can be said on BP 2  to BP 7 . 
     When OE_EVEN is H and OE_ODD is L in the 8-bit bus mode, OUT 0  is outputted to IO 0  while the second output buffer corresponding to IO 1  becomes HiZ. Similarly, OUT 1  is outputted to IO 2 , OUT 2  is outputted to IO 4 , OUT 3  is outputted to IO 6 , OUT 4  is outputted to IO 8 , OUT 5  is outputted to IO 10 , OUT 6  is outputted to IO 12 , and OUT 7  is outputted to IO 14  while the second buffers corresponding to IO 3 , IO 5 , IO 7 , IO 9 , IO 11 , IO 13  and IO 15  become HiZ. 
     When two I/O portions are short-circuited by use of board wiring as shown in  FIG. 6 , current drive capacity of one I/O portion is obtained in BP 0  because one IO 1  of the I/O portions IO 0  and IO 1  connected to BP 0  is HiZ. The same thing can be said on BP 1  to BP 7 , so that current drive capacity of one I/O portion is obtained in each of the BP 1  to BP 7 . 
     Next, an input operation in the 8-bit bus mode in the case of use of board wiring as shown in  FIG. 6  will be described. When OE_EVEN is L, BP 0  is inputted into IN 0  via IO 0 . Similarly, BP 1  is inputted into IN 1  via IO 2 , and BP 2  is inputted IN 2  via  104 . BP 3  to BP 7  are inputted into IN 3  to IN 7  respectively in the same manner as described above. Because IN 8  to IN 15  are not used in the 8-bit bus mode, the signal state of OE_ODD can be neglected. 
     As described above, when controlling is performed in the 8-bit bus mode while the set of output buffers is separated into a set of output buffers corresponding to even-number bits and a set of output buffers corresponding to odd-number bits, either use of one I/O portion per bit or use of two I/O portions per bit can be selected so that current drive capacity can be selected in accordance with the situation. 
     Generally, when output current capacity is high, high frequency can be used because the delay value is small, but noise caused by EMI or the like is high. On the other hand, when output current capacity is low, noise caused by EMI or the like is low but high frequency cannot be used because the delay value is large. Although the operating frequency has a trade-off relation with noise as described above, the output current value can be selected at a point of good balance between the two when configuration is made so that current drive capacity can be selected. 
     Although this embodiment is based on Embodiment 2 and configured so that a function of selecting current drive capacity is added to Embodiment 2, it is a matter of course that this function may be combined with Embodiment 1 for use of outgoing I/O portions. 
     Embodiment 4 
     Although Embodiments 1 to 3 have been described on the case where only OUT 0  to OUT 7  can perform outputting in the 8-bit bus mode, this embodiment is configured so that either use of two I/O portions per bit or use of one I/O portion per bit can be selected as I/O operated in the 8-bit bus mode in the same manner as in Embodiment 3. When use of one I/O portion per bit is selected, the other I/O portion on the unused side is used so that a signal such, as a test signal or an ICE signal different from the ordinary output signal can be outputted. 
       FIG. 4  is a diagram showing the configuration of I/O portions of a semiconductor integrated circuit according to Embodiment 4 of the invention. The semiconductor integrated circuit shown in  FIG. 4  is configured so that the set of output buffers  102  in  FIG. 1  is separated into a first set of output buffers  302 E corresponding to even-number bits and a second set of output buffers  3020  corresponding to odd-number bits, that the first set of output buffers  302 E and the second set of output buffers  3020  are controlled by different signal lines respectively, and that a set of selectors  406  for selecting signals different from the ordinary output signals is added to the configuration shown in  FIG. 1 . 
     OUT 0  to OUT 15  are ordinary output signals generated by the internal operation of the semiconductor integrated circuit and outputted to the outside. OUT 0 P to OUT 7 P are output signals different from the ordinary output signals. MODE 16 B is an output mode switching signal. When MODE 16 B is H, a 16-bit bus mode is selected. When MODE 16 B is L, an 8-bit bus mode is selected. 
     OE_EVEN is an output control signal for controlling the first set of output buffers  302 E. OE_ODD is an output control signal for controlling the second set of output buffers  3020 . When OE_EVEN is H, even-number bits IO 0 , IO 2 , IO 4 , IO 6 , IO 8 , IO 10 , IO 12  and IO 14  are outputted ordinarily. When OE_EVEN is L, the first set of output buffers  302 E become HiZ. When OE_ODD is H, odd-number bits IO 1 , IO 3 , IO 5 , IO 7 , IO 9 , IO 11 , IO 13  and IO 15  are outputted ordinarily. When OE_ODD is L, the second set of output buffers  3020  become HiZ. 
     The operation in the 16-bit bus mode where MODE 16 B is H is the same as in Embodiments 1 to 3. The operation in the 8-bit bus mode where MODE 16 B is L is the same as in Embodiment 1 if OE_EVEN is H, OE_ODD is H and MODEP is L. The operation in the case where OE_EVEN is H and OE_ODD is L is the same as in Embodiment 2 regardless of whether MODEP is L or H. 
     In the 8-bit bus mode where MODE 16 B is L, OUT 0  is outputted to IO 0 , OUT 0 P is outputted to IO 1 , OUT 1  is outputted to IO 2 , OUT 1 P is outputted to IO 3 , OUT 2  is outputted to IO 4 , OUT 2 P is outputted to IO 5 , OUT 3  is outputted to IO 6 , OUT 3 P is outputted to IO 7 , OUT 4  is outputted to IO 8 , OUT 4 P is outputted to IO 9 , OUT 5  is outputted to IO 10 , OUT 5 P is outputted to IO 11 , OUT 6  is outputted to IO 12 , OUT 6 P is outputted to IO 13 , OUT 7  is outputted to IO 14 , and OUT 7 P is outputted to IO 15  if OE_EVEN is H, OE_ODD is H and MODEP is H. 
     As described above, selection of either current drive capacity of one I/O portion per bit or current drive capacity of two I/O portions per bit can be controlled by OE_ODD in the 8-bit bus mode. Moreover, while current drive capacity of one I/O portion per bit is selected on the basis of MODEP&#39;s control, the other I/O portion can be used for outputting another signal. 
     Although this embodiment is configured so that I/O portions are used as outgoing I/O portions, it is a matter of course that this embodiment may be combined with Embodiment 3 so that I/O portions are used as bidirectional I/O portions. 
     Embodiment 5 
       FIG. 5  is a diagram showing the configuration of I/O portions of a semiconductor integrated circuit according to Embodiment 5 of the invention. This embodiment is configured so that ascending order of I/O can be switched over to descending order, and vice versa, and that a set of selectors  507  for switching ascending order of I/O over to descending order are added to the configuration shown in  FIG. 1 . 
     MODE 16 B is an output mode switching signal. When MODE 16 B is H, a 16-bit bus mode is selected. When MODE 16 B is L, an 8-bit bus mode is selected. OE is an output control signal. When OE is H, IO 0  to IO 15  are outputted ordinarily. When OE is L, the set of output buffers  102  for IO 0  to IO 15  become HiZ. FLIP is a control signal given to the set of selectors  507  for selecting either ascending order or descending order of I/O. 
     When MODE 16 B is H and FLIP is L, a normal 16-bit bus mode is selected. If OE is H, OUT 0  to OUT 15  are outputted to IO 0  to IO 15  directly. When MODE 16 B is H and FLIP is H, an inverted 16-bit bus mode is selected. If OE is H, the bit order of OUT 0  to OUT 15  is inverted so that OUT 0  to OUT 15  are outputted to IO 15  to IO 0  respectively. 
     When MODE 16 B is L and FLIP is L, a normal 8-bit bus mode is selected. If OE is H, OUT 0  is outputted to IO 0  and IO 1 , OUT 1  is outputted to IO 2  and IO 3 , OUT 2  is outputted to IO 4  and IO 5 , OUT 3  is outputted to IO 6  and IO 7 , OUT 4  is outputted to IO 8  and  109 , OUT 5  is outputted to IO 10  and IO 11 , OUT 6  is outputted to IO 12  and IO 13 , and OUT 7  is outputted to IO 14  and IO 15 . 
     When two I/O portions are short-circuited by use of board wiring as shown in  FIG. 6  in the same manner as in Embodiment 1, BP 0  is connected to IO 0  and IO 1  so that current drive capacity of two outgoing I/O portions is obtained in accordance with OUT 0 . BP 1  is connected to IO 2  and IO 3  so that current drive capacity of two outgoing I/O portions is obtained in accordance with OUT 1 . The same thing can be said on BP 2  to BP 7 . 
     When MODE 16 B is L and FLIP is H, an inverted 8-bit bus mode is selected. If OE is H, OUT 0  is outputted to IO 15  and IO 14 , OUT 1  is outputted to IO 13  and IO 12 , OUT 2  is outputted to IO 11  and IO 10 , OUT 3  is outputted to IO 9  and IO 8 , OUT 4  is outputted to IO 7  and IO 6 , OUT 5  is outputted to IO 5  and IO 4 , OUT 6  is outputted to IO 3  and IO 2 , and OUT 7  is outputted to IO 1  and IO 0 . 
     Also in this case, when two I/O portions are short-circuited by use of board wiring as shown in  FIG. 6 , BP 0  is connected to IO 0  and IO 1  so that current drive capacity of two outgoing I/O portions is obtained in accordance with OUT 7 . BP 1  is connected to IO 2  and IO 3  so that current drive capacity of two outgoing I/O portions is obtained in accordance with OUT 6 . The same thing can be said on BP 2  to BP 7 . 
     Although this embodiment is based on Embodiment 1, it is a matter of course that this embodiment may be combined with any one of Embodiments 2 to 4. 
     The semiconductor integrated circuit according to the invention has an effect of reducing the value of output delay to make a high-speed operation possible because current drive capacity can be improved without use of any special external output circuit in an output mode with a small bus width in a semiconductor integrated circuit having a plurality of output modes with variable bus widths. The semiconductor integrated circuit according to the invention is useful as a semiconductor integrated circuit etc. having a plurality of output modes with variable bus widths.

Technology Category: h