I believe you do write the entire 256 bytes out (all zeros in this case). Here's what the packet looks like:

Packet Header (every packet has this):
1: PSOH
2-3: data size (num bytes in packet body, 268 in this case)
4: opcode (0x0C for command)
5: type (0x00 for request)
6-9: packet ID (unique counter for packet; starts at 42)

Command Request Packet
10-13: command (0x00 - restart)
14-17: param 1 (0x01 - restart player)
15-18: param 2 (0x00)
19-274: empty byte array

Closing:
275-276: crc