SXFER_REG
host, SXFER_REG);
SCp->device->host, SXFER_REG);
synchronous = NCR_700_readb(host, SXFER_REG) & 0x0f;
NCR_700_writeb(ASYNC_OPERATION, host, SXFER_REG);
host, SXFER_REG);