ar1100t-i/ml Microchip Technology Inc., ar1100t-i/ml Datasheet - Page 17

• Manufacturer Part Number: ar1100t-i/ml
• Description: Ar1100 Resistive Usb And Rs-232 Touch Screen Controller
• Manufacturer: Microchip Technology Inc.

4.2.2.1
GENERAL
The generic framework for all packets
comprised of a SYNC byte, a SIZE byte and a DATA
section. The DATA section has a maximum size of 255
total bytes.
FIGURE 4-1:
COMMAND
A COMMAND packet has a minimum of 3 bytes
defined as SYNC, SIZE and CMND. The DATA section
is command-dependant and can include up to 254
associated data bytes (D[1] – D[N]). See
FIGURE 4-2:
RESPONSE
A RESPONSE packet has a minimum of 4 bytes
defined as SYNC, SIZE, STATUS and CMND. As with
the COMMAND packet, the RESPONSE packet is
command-dependant and can include up to 253 asso-
ciated data bytes. In cases where the RESPONSE
packet is in direct response to a COMMAND packet,
the CMND byte is the same in both.
FIGURE 4-3:
4.2.2.2
In UART communication mode a complete COMMAND
packet must be delivered before the packet ‘time-out’
timer expires (~250 msec). A packet ‘time out’ will
cause any partial packet to be discarded and the
packet parsing state controller to reset. Using this
mechanism, the host can always ensure (re-establish)
‘SYNC’ by pausing for 250+ msec before sending
another packet.
 2011 Microchip Technology Inc.
SYNC
0x55
AR1100 RESISTIVE USB AND RS-232 TOUCH SCREEN CONTROLLER
Construction
Mode: UART
SIZE
N
PACKET FORMAT –
GENERAL
PACKET FORMAT – COMMAND
PACKET FORMAT – RESPONSE
SYNC
0x55
SYNC
0x55
D[1]
DATA
SIZE
N+2
(Figure
SIZE
Figure
N+1
D[N]
4-1) is
STATUS
4-2.
Preliminary
CMND
CMND
4.2.2.3
Typically, a packet arrives (and is delivered) in a single,
64-byte (max.) USB buffer. Theoretically, a COMMAND
packet can span multiple, physical USB buffers but will
be subject to the packet time-out criteria described in
the UART section. A RESPONSE packet will always be
delivered in a single buffer and a buffer will never
contain more than one.
D[1]
DATA
DATA
D[1]
Mode: USB
D[N]
D[N]
DS41606A-page 17