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 . fig1 is a diagram showing the configuration of i / o portions of a semiconductor integrated circuit according to embodiment 1 of the invention . in fig1 , 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 . fig6 shows an example of configuration in the case where two outgoing i / o portions are short - circuited by use of board wiring . in fig6 , 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 . 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 . fig2 is a diagram showing the configuration of i / o portions of a semiconductor integrated circuit according to embodiment 2 of the invention . in fig2 , 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 fig6 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 . 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 . fig3 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 fig3 is configured so that the set of output buffers 102 in embodiment 2 shown in fig2 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 fig6 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 fig6 , 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 fig6 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 . 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 . fig4 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 fig4 is configured so that the set of output buffers 102 in fig1 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 fig1 . 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 . fig5 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 fig1 . 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 fig6 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 fig6 , 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 .