12.2 Clock Architecture Description

CY7C601xx, CY7C602xx

When using the 32 kHz oscillator, the PITMRL/H is read until two consecutive readings match before sending and receiving data. The following firmware example assumes the developer is interested in the lower byte of the PIT.

Read_PIT_counter: mov A, reg[PITMRL] mov [57h], A

mov A, reg[PITMRL] mov [58h],A

mov [59h], A

mov A, reg[PITMRL] mov [60h], A

;;;Start comparison mov A,[60h]

mov X, [59h] sub A, [59h] jz done mov A, [59h] mov X, [58h] sub A, [58h] jz done mov X, [57h]

;;;correct data is in memory location 57h done:

mov [57h], X ret

The CY7C601xx part is optionally sourced from an external crystal oscillator. The external clock driving on CLKIN range is from 187 KHz to 24 MHz.

12.2 Clock Architecture Description

The enCoRe II LV clock selection circuitry allows the selection of independent clocks for the CPU, Interval Timers, and Capture Timers.

On the CY7C601xx, the external oscillator is sourced by the crystal oscillator. When the crystal oscillator is disabled, it is sourced directly from the CLKIN pin. The external crystal oscillator is fed through the EFTB block, which is optionally bypassed.

12.2.1 CPU Clock

The CPU clock, CPUCLK, is sourced from the external crystal oscillator, the internal 24 MHz oscillator, or the Internal 32 kHz low power oscillator. The selected clock source can optionally be divided by 2n-1where n is 0–7 (see Table 12-3).

When it is not being used by the external crystal oscillator, the CLKOUT pin is driven from one of many sources. This is used for test and also in some applications. The sources that drive the CLKOUT are:

CLKIN after the optional EFTB filter.

Internal 24 MHz Oscillator.

Internal 32 kHz Oscillator.

CPUCLK after the programmable divider.

Document 38-16016 Rev. *E

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Cypress manual Clock Architecture Description, CPU Clock, CY7C601xx, CY7C602xx