© 2014 Exar Corporation
XR22801
33 / 40 exar.com/XR22801
Rev 1A
HID Register Descriptions
Note that all register reset default values are ’0’ unless otherwise specified. All registers are 16 bits.
I
2
C_SCL_LOW (0x341) - Read/Write
I
2
C_SCL_HIGH (0x342) - Read/Write
EDGE_FUNC_SEL (0x3C0) - Read/Write
EDGE_DIR (0x3C1) - Read/Write
Note that when setting direction of an EDGE IO to output, the EDGE_PULL_UP for that IO pin should also be disabled and
when setting an EDGE IO pin to input, the EDGE_PULL_UP for that IO pin should also be enabled.
Bit Default Description
15:0 0x0144
Value
Specifies the number of periods that SCL will be asserted low by the XR22801 I
2
C master. Note that in clock
stretching, the I
2
C slave may extend the SCL low period to delay the next transaction. For 100 kbps transfer
rate this value must be at least 252 (0x00FC) and the sum of high and low periods must be at least 600
(0x0258). For 400kbps transfer rate this value must be at least 78 (0x004E) and the sum of the high and low
periods must be at least 150 (0x0096). Measured in 60 MHz core clock periods, i.e. approximately 16.7 ns.
Bit Default Description
15:0 0x0114
Value
Specifies the number of periods that SCL will be asserted high by the XR22801 I
2
C master. Note that another
multi-master may assert SCL low before the XR22801 high period is completed. For 100 kbps transfer rate this
value must be at least 240 (0x00F0) and the sum of the high and low periods must be at least 600 (0x0258).
For 400 kbps transfer rate this value must be at least 36 (0x0024) and the sum of the high and low periods must
be at least 150 (0x0096). Measured in 60 MHz core clock periods, i.e. approximately 16.7 ns
Bit Default Description
15:8 0xFF
Reserved
These bits are reserved and should be written as ‘1’.
7:0 0x00
E[7:0]
0: IO is assigned to the UART / GPIO function. IO pin controlled using UART registers.
1: IO is assigned to the EDGE function. IO pin controlled using EDGE registers.
Bit Default Description
15:8 0x00
Reserved
These bits are reserved and should be written as ‘0’.
7:0 0x00
E[7:0]
0: IO pin assigned to EDGE function is configured as an input
1: IO pin assigned to EDGE function is configured as an output.
