HD64570 Datasheet, PDF (329/469 Pages) Hitachi Semiconductor – Serial Communications Adaptor

7.7 Precautions
When using the timer, keep the following in mind:
• Clear the TME bit of the timer control/status register (TCSR) before changing the timer
operating clock.
• Reserved bits of the TCSR and the timer expand prescale register (TEPR) always read 0.
Rev. 0, 07/98, page 313 of 453