SEGA SATURN DEVELOPER'S MANUAL

3.2 Communication method
(1) Communication time: All interrupts are prohibited during the command / response response time. Response time may be delayed if commands are issued continuously.
(2) Communication error If the CD block does not respond within the specified time after issuing the: command, a communication timeout error will occur. Whether or not there is a response is determined by polling a fixed number of times using a software loop.
(3) Command issue rules The: command must be issued according to the following rules.
(A) The maximum number of commands that can be issued in any 6.7ms is 30 times.
(B) The maximum number of commands that can be issued within 16.7ms is 60 times.
(C) When acquiring subcodes, commands can be issued up to 34 times in any 13.3ms.
(Acquire 16 subcodes R to W + 1 subcode Q: 17 x 2 = 34 times in total)
(D) Commands belonging to the same command end flag are issued after the end of processing.

ポーリング Polling processing by issuing commands continuously is prohibited.
To poll for state changes, use a periodic response or interrupt factor register. In addition, commands are issued using the timing of SCDQ, CSCT flag, VSYNC, etc.

3.2 Communication method