MC68HC05JJ6 Datasheet, PDF (145/216 Pages) Freescale Semiconductor, Inc – General Release Specification Microcontrollers

Simple Serial Interface
9.4.3 SIOP Data Register
The SIOP data register (SDR) is located at address $000C and serves
as both the transmit and receive data register. Writing to this register will
initiate a message transmission if the node is in master mode. The SIOP
subsystem is not double buffered and any write to this register will
destroy the previous contents. The SDR can be read at any time.
However, if a transfer is in progress, the results may be ambiguous.
Writing to the SDR while a transfer is in progress can cause invalid data
to be transmitted and/or received. Figure 9-6 shows the position of each
bit in the register. This register is not affected by reset.
$000C Bit 7
6
5
4
3
2
1
Bit 0
Read:
Bit 7
6
5
4
3
2
1
Bit 0
Write:
Reset:
Unaffected by Reset
Figure 9-6. SIOP Data Register (SDR)
MC68HC05JJ6/MC68HC05JP6 — Rev. 3.2
Freescale Semiconductor
Simple Serial Interface
General Release Specification
145