pc87591l National Semiconductor Corporation, pc87591l Datasheet - Page 239

• Manufacturer Part Number: pc87591l
• Description: Lpc Mobile Embedded Controllers
• Manufacturer: National Semiconductor Corporation

Revision 1.07
Embedded Controller Modules
4.18 HIGH-FREQUENCY CLOCK GENERATOR (HFCG)
The HFCG generates the high-frequency clock (OSCCLK) based on the system’s 32.768 KHz clock signal. The HFCG out-
put is derived from OSCCLK and generates the host domain clock and the core domain clock. Clock generation is controlled
by the core domain’s PMC module (see Section 4.17 on page 235) and the host domain’s SuperI/O configuration (see
Section 6 on page 335).
To generate OSCCLK, the HFCG includes a programmable frequency multiplier. The core domain clock is derived from
OSCCLK via a programmable pre-scaler; its frequency is in the range of 4 MHz to 20 MHz. The host domain clock is derived
from OSCCLK via a pre-scaler that divides by 2, generating an output of 48 MHz (see Figure 78).
4.18.1 Features
4.18.2 Functional Description
Figure 78 shows the HFCG blocks.
The frequency multiplier includes a 5-bit variable (N) and a 14-bit variable (M); these variables define the OSCCLK frequen-
cy. There are two software methods to set the frequency of OSCCLK (by changing N and M); the method used depends on
the HFCG state, as described in Section 4.18.3. The methods are:
Software Method 1. Write new values (HFCGML, HFCGMH and HFCGN registers) to a buffer and enable the programma-
ble frequency setting. Either a normal or fast clock setting may be used. The programmable pre-scaler of the core domain
clock is automatically set to a divide by 1; see “PMC Enabled SuperI/O Disabled State” on page 240.
Programmable frequency multiplier for a wide range of output frequencies
Core domain clock and host domain clock generation
Programmable pre-scaler to derive the core domain clock from OSCCLK
Separate enable/disable for core domain clock and host domain clock
On V
— 4 MHz default core domain clock frequency is set
— Host domain clock is disabled
On WATCHDOG reset and Debugger Interface reset:
— If host domain clock is enabled, the 48 MHz clock monitor is initiated
— If host domain clock is disabled, the 4 MHz default core domain clock frequency is set
32 KHz
Enable from SuperI/O
Enable from PMC
Hardwired Settings
Parameter Settings
Host Domain
CC
N, M, I for
= Software
= Includes software-accessible registers
N, M, I
power-up:
Control and Status
Figure 78. HFCG Schematic Diagram
(Continued)
Frequency
Multiplier
239
OSCCLK
Programmable
Divide by 2
Pre-Scaler
Current Settings
N, M, I
Host Domain
Clock
Core Domain
Clock
INT to ICU
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