Renesas Stereo System SH7709S User Manual

Rev. 5.00, 09/03, page 389 of 760

Section 12   Timer (TMU)

The SH7709S has a three-channel (channels 0 to 2) 32-bit timer unit (TMU).

The TMU has the following features:

•

 

Each channel is provided with an auto-reload 32-bit down counter.

•

 

Channel 2 is provided with an input capture function.

•

 

All channels are provided with 32-bit constant registers and 32-bit down counters that can be
read or written to at any time.

•

 

All channels generate interrupt requests when the 32-bit down counter underflows
(H'00000000 

→

 H'FFFFFFFF).

•

 

Allows selection between 6 counter input clocks: External clock (TCLK), on-chip RTC output
clock (16 kHz), P

φ

/4, P

φ

/16, P

φ

/64, P

φ

/256. (P

φ

 is the internal clock for peripheral modules.)

See section 9, On-Chip Oscillation Circuits, for more information on the clock pulse generator.

•

 

All channels can operate when the SH7709S is in standby mode: When the RTC output clock
is being used as the counter input clock, the SH7709S is still able to count in standby mode.

•

 

Synchronized read: TCNT is a sequentially changing 32-bit register. Since the peripheral
module used has an internal bus width of 16 bits, a time lag can occur between the time when
the upper 16 bits and lower 16 bits are read. To correct the discrepancy in the counter read
value caused by this time lag, a synchronization circuit is built into the TCNT so that the entire
32-bit data in the TCNT can be read at once.

•

 

The maximum operating frequency of the 32-bit counter is 2 MHz on all channels: Operate the
SH7709S so that the clock input to the timer counters of each channel (obtained by dividing
the external clock and internal clock with the prescaler) does not exceed the maximum
operating frequency.