Cypress CY7C638xx manual Clocking, Checksum Function, Checksum Parameters Name Address Description

CY7C63310, CY7C638xx

9.5.8 Checksum Function

The Checksum function calculates a 16-bit checksum over a user specifiable number of blocks, within a single Flash macro (Bank) starting from block zero. The BLOCKID parameter is used to pass in the number of blocks to calculate the checksum over. A BLOCKID value of 1 calculates the checksum of only block 0, while a BLOCKID value of 0 calculates the checksum of all 256 user blocks. The 16-bit checksum is returned in KEY1 and KEY2. The parameter KEY1 holds the lower eight bits of the checksum and the parameter KEY2 holds the upper eight bits of the checksum.

The checksum algorithm executes the following sequence of three instructions over the number of blocks times 64 to be checksummed.

romx

add [KEY1], A adc [KEY2], 0

Table 9-12. Checksum Parameters

Name	Address	Description
KEY1	0,F8h	3Ah
KEY2	0,F9h	Stack Pointer value when SSC is
		executed.
BLOCKID	0,FAh	Number of Flash blocks to calculate
		checksum on.

When using the 32 kHz oscillator, the PITMRL/H registers must be read until 2 consecutive readings match before the result is considered valid. 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

10. Clocking

The enCoRe II has two internal oscillators, the Internal 24 MHz Oscillator and the 32 kHz Low power Oscillator.

The Internal 24 MHz Oscillator is designed such that it may be trimmed to an output frequency of 24 MHz over temperature and voltage variation. With the presence of USB traffic, the Internal 24 MHz Oscillator may be set to precisely tune to the USB timing requirements (24 MHz ± 1.5%). Without USB traffic, the Internal 24 MHz Oscillator accuracy is 24 MHz ± 5% (between 0°–70°C). No external components are required to achieve this level of accuracy.

The internal low speed oscillator of nominally 32 kHz provides a slow clock source for the enCoRe II in suspend mode, particu- larly to generate a periodic wakeup interrupt and also to provide a clock to sequential logic during power up and power down events when the main clock is stopped. In addition, this oscillator can also be used as a clocking source for the Interval Timer clock (ITMRCLK) and Capture Timer clock (TCAPCLK). The 32 kHz Low power Oscillator can operate in low power mode or can provide a more accurate clock in normal mode. The Internal

32kHz Low power Oscillator accuracy ranges (between 0°–70° C) follow:

■5V Normal mode: –8% to + 16%

■5V LP mode: +12% to + 48%

Document 38-08035 Rev. *K Page 19 of 83

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