Re: Interrupt modes?? (coding question)

[Richard Gerrits]

>Though, when you build such a device you should make sure that > you only have one such device in your computer. If you put a second one in > the second cartridge slot for example, you will get bus conflicts if they > generate an interrupt at the same time... Or to be more precise, if they both > generate an interrupt before the Z80 acknowledges it (the interrupt does not > get acknowledged as long as the Z80 is in DI mode...) IMO this is not completely true. I found the device at the end of this email in a book about Z80 assembler. It has 4 switches each combined with a R-S flipflop (based on 2 NAND ports). When switch s0 is pressed, input 0 of the 8to3 encoder (74148) becomes low. Outputs A, B and C become high. OE' becomes low and this triggers the J-K flipflop (74LS73). Q' becomes low and thus INT' also becomes low and a interrupt is requested.   When the Z80 acknowledges it ( by lowering M1' and IORQ' ), the busdriver (74367) puts the data on the bus (in this case FEh) and the J-K flipflop is reset.   s0 -> interrupt FE s1->  interrupt FC s2->  interrupt FA s3->  interrupt F8     Each switch can thus execute a different interruptroutine.   A program example:   LD HL, ADRES_ROUTINE1 LD 1BFE, HL                        ; to int. vector FEh LD HL, ADRES_ROUTINE2 LD 1BFC, HL                        ; to int. vector FCh LD HL, ADRES_ROUTINE3 LD 1BFA, HL                        ; to int. vector FAh LD HL, ADRES_ROUTINE4 LD 1BF8, HL                        ; to int. vector F8h IM 2                                    ; interrupt mode 2 LD A, 1B                             ; MSB of int. vector table LD I,A                                 ; Put it in int. register     DISCLAIMER: I didn't test the circuit, it neither is specificly designed for a MSX. But I think it should work.   Greetings Richard [EMAIL PROTECTED]   PS You need the font "courrier" (and your imagination) the read the circuit below.                                                                                                                                                74148                                                 gnd                                             ___|______                                            |7  E'     |          74367                7400                        |6         |              _________                     |5        C|        _________        _____|I1       |                    |4         |        |       |        |    |  NAND O1|____________________|3        B|________|I2   O2|______D2        |  __|I2       | |  ________________|2         |        |       |        .  | |---------| |  |   ____________|1        A|________|I1   O1|______D1     s3/   \  ___________|  |  |  __________|0         |        |       | gnd--/     \/              |  |  |         |          |    gnd_|I0   O0|______D0            /\___________   |  |  |         | OE'  OE  |        |       |        .  /  _________  |  |  |  |         --|---------        | CE'   |        |  |_|I1       | |  |  |  |      _____| __________      ---|-----        |    |  NAND O1|_|  |  |  |      |      |         |        |        |____|I2       |    |  |  |      |  +5V-|J      Q |        |             |---------|    |  |  |      |------|>        |        |                            |  |  |         gnd-|K      Q'|--INT'  |                            |  |  |             |   CLK   |        |              _________     |  |  |             |---------|        |        _____|I1       |    |  |  |                 |______________|        |    |  NAND O1|____|  |  |                          |       7432        |  __|I2       | |     |  |               ^          |    _________        .  | |---------| |     |  |               |          |    |     I1|_M1'     s2/   \  ___________|     |  |             74LS73       |____|O1 OR  | gnd--/     \/                 |  |                               |     I2|_IORQ'            /\___________      |  |                               |-------|        .  /  _________  |     |  |        |  |_|I1       | |     |  |        |    |  NAND O1|_|     |  |        |____|I2       |       |  |             |---------|       |  |                               |  |                               |  |                               |  |                               |  |              _________        |  |        _____|I1       |       |  |        |    |  NAND O1|_______|  |        |  __|I2       | |        |        .  | |---------| |        |     s1/   \  ___________|        | gnd--/     \/                    |            /\___________         |        .  /  _________  |        |        |  |_|I1       | |        |        |    |  NAND O1|_|        |        |____|I2       |          |             |---------|          |                                  |              _________           |        _____|I1       |          |        |    |  NAND O1|__________|        |  __|I2       | |        .  | |---------| |     s0/   \  ___________| gnd--/     \/            /\___________        .  /  _________  |        |  |_|I1       | |        |    |  NAND O1|_|        |____|I2       |             |---------|