Intel 8XC196MD, 8XC196MH Issuing the Reset RST Instruction, Issuing an Illegal Idlpd Key Operand

8XC196MC, MD, MH USER’S MANUAL

13.6.2 Issuing the Reset (RST) Instruction

The RST instruction (opcode FFH) resets the device by pulling RESET# low for 16 state times. It also clears the processor status word (PSW), sets the master program counter (PC) to 2080H, and resets the special function registers (SFRs). See Table C-2 on page C-2 for the reset values of the SFRs.

Putting pull-ups on the address/data bus causes unimplemented areas of memory to be read as FFH. If unused internal OTPROM memory is set to FFH, then execution from any unused mem- ory locations will reset the device.

13.6.3 Issuing an Illegal IDLPD Key Operand

The device resets itself if an illegal key operand is used with the idle/powerdown (IDLPD) com- mand. The legal keys are “1” for idle mode and “2” for powerdown mode. If any other value is used, the device executes a reset sequence. (See Appendix A for a description of the IDLPD com- mand.)

13.6.4 Generating Wait States

The 8XC196Mx devices can interface with a variety of external memory devices. With slower external devices this requires inserting wait states to lengthen the bus cycle. An external device can use the READY input to request wait states in addition to the wait states that are generated

internally by the 8XC196Mx device. The READY signal must be held valid until the TCLYX (for the 8XC196MC, MD) or TLLYX (for the 8XC196MH) timing specification is met. Do not exceed

the maximum TCLYX (for the 8XC196MC, MD) or TLLYX (for the 8XC196MH) specification or additional (unwanted) wait states might be added (see Chapter 15, “Wait States (Ready Control),”

for a detailed explanation).

13.6.5 Enabling the Watchdog Timer

The watchdog timer (WDT) is a 16-bit counter that resets the device when the counter overflows. The WDE bit (bit 3) of CCR1 controls whether the watchdog is enabled immediately or is dis- abled until the first time it is cleared. Clearing WDE activates the watchdog. Setting WDE makes the watchdog timer inactive, but you can activate it by clearing the watchdog register. Once the watchdog is activated, only a reset can disable it.

The 8XC196MC and 8XC196MD allow only one reset interval, 64K state times. This requires your software to interrupt itself every 65,535 state times to reset the watchdog. The 8XC196MH allows you to choose a longer interval.

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