Holtek HT66F20 Manual page 239

HT66F20/HT66F30/HT66F40/HT66F50/HT66F60
HT66FU30/HT66FU40/HT66FU50/HT66FU60
A/D Flash MCU with EEPROM
UART Module SPI Interface
The MCU communicates with the UART Module via an internal SPI interface. The SPI interface on
this device is comprised of four signals: SCS (SPI Chip Select), SCK (SPI Clock), SDI (Serial Data
Input) and SDO (Serial Data Output). The SPI master, which is the MCU, asserts SCS by pulling it
low to start the data transaction cycle. When the first 8 bits of data are transmitted, SCS should not
return to a high level. Instead, SCS must remain at a low level until the whole 16-bit data transaction
is completed. If SCS is de-asserted, that is returned to a high level before the 16-bit data transaction
is completed, all data bits will be discarded by the UART Module SPI slave.
SPI Timing
Both read and write operations are conducted along the SPI common interface with the following
format:
• Write Type Format: 8-bit command input + 8-bit data input
• Read Type Format: 8-bit command input + 8-bit data output
SCS
SCK
SDI
A� A6 A5 A4
SDO
Writing Type Format: 8-bit Command Input + 8-bit Data Input
SCS
SCK
SDI A� A6 A5 A4
SDO
Reading Type Format: 8-bit Command Input + 8-bit Data Output
Rev. 2.50
V
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V D D
S C K S C K
S D O S D I
S D I S D O
M C U
S C S S C S
P I N T I N T
P C K C L K I
G N D
MCU to UART Internal Connection
Note: PCK output frequency must be ≤ 12MHz.
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239
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