ZBasicSysLib - page 19 of 295

ZBasic System Library

ZX Microcontroller Family

interrupts for every bit received so the situation is much more problematic. In this case, having interrupts

disabled for longer than approximately one-third of the bit time will likely cause garbled input if a

character’s transmit time overlaps the period when interrupts are disabled. For characters being

transmitted by channels 3-6, having interrupts disabled for more than about 10% of the bit time may

cause the receiver to lose synchronization.

For reference purposes, the table below indicates which I/O routines disable interrupts for the duration of

their execution. See the individual descriptions for more detailed information.

System Library Routines that Disable Interrupts

CountTransitions

Interrupt Service Routines

For the native code devices (e.g. ZX-24n), a few interrupt service routines (ISRs) are always included in

your program (e.g. for Com1 and the RTC) while others are included only if certain System Library

routines are used in your program. In some cases, the additional ISRs that are included when a specific

System Library routine is used depends on how the routine is invoked and what the compiler can deduce

regarding which ISRs might be needed. For example, if OpenCom() is invoked one or more times but the

compiler can determine that the Com1 is always the channel being used, no additional ISRs are included

since the Com1 ISRs are always included. On the other hand, if the compiler cannot determine which

channel is being opened in one or more cases, it includes the ISRs for all Com channels, both hardware-

based and software-based channels.

In the description of each System Library routine, information is given about the set of ISRs might be

included in your program if you use that routine. This information is only important, of course, if you are

also providing one or more ISRs in your code because conflicts may arise. (See the section entitled

“Defining Interrupt Service Routines” in the ZBasic Language Reference Manual for more information on

how this is done.) The table below gives an overview of which System Library routines may cause ISRs

to be included atomatically in your program. The shaded entries represent ISRs that are always included.

System Library Routines that May Load ISRs

Timer1_CompA Timer1_CompA Timer1_CompA Timer4_CompA Timer4_CompA

Timer1_CompA Timer1_CompA Timer1_CompA Timer4_CompA Timer4_CompA