Scali mentioned a Counter can be used for muting, but i need to cut the SN76489 from ISA Bus to send the commands right ?
if not i will send the data to the whole bus ?
Yup, you won't want to have the commands 'leak' onto the ISA bus.
Is there a way to lock bus for a few ms do send the commands ?
I don't know the details of all ISA communication, but as far as I understand it, a DMA transfer is the only way an ISA card can initiate anything. Any other operation can only be done in response to the CPU/motherboard initiating any kind of read/write operation, where you can insert wait states.
So perhaps you can 'fake' a DMA transfer, this is how cards tended to implement bus mastering back in the day. See at the bottom of this page:
My idea was that it may be simpler to solve it on the card itself, so you multiplex the data and control lines.
Eg, if you have some and-ports, you can have a single bit select either the ISA pins as input, or the counter circuit. This way the chip is either connected to the ISA pins, or to the counter circuit, but never both at the same time. Also the counter is never connected to the ISA pins.