Memory Map and Registers

 

 

Table 20-8. GPTCNT Field Descriptions

 

 

 

Bit(s)

Name

Description

 

 

 

15–0

CNTR

Read-only field that provides the current count of the timer counter. To ensure coherent

 

 

reading of the timer counter, such that a timer rollover does not occur between two

 

 

back-to-back 8-bit reads, it is recommended that only word (16-bit) accesses be used.

 

 

A write to GPTCNT may have an extra cycle on the first count because the write is not

 

 

synchronized with the prescaler clock. The write occurs at least one cycle before the

 

 

synchronization of the prescaler clock.

 

 

These bits are read anytime. They should be written to only in test (special) mode;

 

 

writing to them has no effect in normal modes.

 

 

 

20.5.6 GPT System Control Register 1 (GPTSCR1)

Field

Reset

R/W

Address

7

6

5

4

3

0

GPTEN

 

TFFCA

 

 

 

 

 

 

 

0000_0000

R/W

IPSBAR + 0x1A_0006, 0x1B_0006

Figure 20-7. GPT System Control Register 1 (GPTSCR1)

Table 20-9. GPTSCR1 Field Descriptions

Bit(s)

Name

 

Description

 

 

 

7

GPTEN

Enables the general purpose timer. When the timer is disabled, only the registers are

 

 

accessible. Clearing GPTEN reduces power consumption. These bits are read

 

 

anytime, write anytime.

 

 

1

GPT enabled

 

 

0

GPT and GPT counter disabled

 

 

 

6–5

Reserved, should be cleared.

 

 

 

4

TFFCA

Timer fast flag clear all. Enables fast clearing of the main timer interrupt flag registers

 

 

(GPTFLG1 and GPTFLG2) and the PA flag register (GPTPAFLG). TFFCA eliminates

 

 

the software overhead of a separate clear sequence. See Figure 20-8.

 

 

When TFFCA is set:

 

 

An input capture read or a write to an output compare channel clears the

 

 

 

corresponding channel flag, CxF.

 

 

Any access of the GPT count registers (GPTCNTH/L) clears the TOF flag.

 

 

Any access of the PA counter registers (GPTPACNT) clears both the PAOVF and

 

 

 

PAIF flags in GPTPAFLG.

 

 

Writing logic 1s to the flags clears them only when TFFCA is clear.

 

 

1

Fast flag clearing

 

 

0

Normal flag clearing

 

 

 

3–0

Reserved, should be cleared.

 

 

 

 

20-8

MCF5282 User’s Manual

MOTOROLA

Page 430
Image 430
Motorola MCF5282, MCF5281 user manual GPT System Control Register 1 GPTSCR1, Gptcnt Field Descriptions, Gpten Tffca